/* png.c - location for general purpose libpng functions * * Copyright (c) 2018-2024 Cosmin Truta * Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson * Copyright (c) 1996-1997 Andreas Dilger * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc. * * This code is released under the libpng license. * For conditions of distribution and use, see the disclaimer * and license in png.h */ #include "pngpriv.h" /* Generate a compiler error if there is an old png.h in the search path. */ Your_png_h_is_not_version_1_6_43; /* Tells libpng that we have already handled the first "num_bytes" bytes * of the PNG file signature. If the PNG data is embedded into another * stream we can set num_bytes = 8 so that libpng will not attempt to read * or write any of the magic bytes before it starts on the IHDR. */ #ifdef PNG_READ_SUPPORTED void PNGAPI png_set_sig_bytes(png_structrp png_ptr, int num_bytes) { … } /* Checks whether the supplied bytes match the PNG signature. We allow * checking less than the full 8-byte signature so that those apps that * already read the first few bytes of a file to determine the file type * can simply check the remaining bytes for extra assurance. Returns * an integer less than, equal to, or greater than zero if sig is found, * respectively, to be less than, to match, or be greater than the correct * PNG signature (this is the same behavior as strcmp, memcmp, etc). */ int PNGAPI png_sig_cmp(png_const_bytep sig, size_t start, size_t num_to_check) { … } #endif /* READ */ #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) /* Function to allocate memory for zlib */ PNG_FUNCTION(voidpf /* PRIVATE */, png_zalloc,(voidpf png_ptr, uInt items, uInt size),PNG_ALLOCATED) { … } /* Function to free memory for zlib */ void /* PRIVATE */ png_zfree(voidpf png_ptr, voidpf ptr) { … } /* Reset the CRC variable to 32 bits of 1's. Care must be taken * in case CRC is > 32 bits to leave the top bits 0. */ void /* PRIVATE */ png_reset_crc(png_structrp png_ptr) { … } /* Calculate the CRC over a section of data. We can only pass as * much data to this routine as the largest single buffer size. We * also check that this data will actually be used before going to the * trouble of calculating it. */ void /* PRIVATE */ png_calculate_crc(png_structrp png_ptr, png_const_bytep ptr, size_t length) { … } /* Check a user supplied version number, called from both read and write * functions that create a png_struct. */ int png_user_version_check(png_structrp png_ptr, png_const_charp user_png_ver) { … } /* Generic function to create a png_struct for either read or write - this * contains the common initialization. */ PNG_FUNCTION(png_structp /* PRIVATE */, png_create_png_struct,(png_const_charp user_png_ver, png_voidp error_ptr, png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr, png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED) { … } /* Allocate the memory for an info_struct for the application. */ PNG_FUNCTION(png_infop,PNGAPI png_create_info_struct,(png_const_structrp png_ptr),PNG_ALLOCATED) { … } /* This function frees the memory associated with a single info struct. * Normally, one would use either png_destroy_read_struct() or * png_destroy_write_struct() to free an info struct, but this may be * useful for some applications. From libpng 1.6.0 this function is also used * internally to implement the png_info release part of the 'struct' destroy * APIs. This ensures that all possible approaches free the same data (all of * it). */ void PNGAPI png_destroy_info_struct(png_const_structrp png_ptr, png_infopp info_ptr_ptr) { … } /* Initialize the info structure. This is now an internal function (0.89) * and applications using it are urged to use png_create_info_struct() * instead. Use deprecated in 1.6.0, internal use removed (used internally it * is just a memset). * * NOTE: it is almost inconceivable that this API is used because it bypasses * the user-memory mechanism and the user error handling/warning mechanisms in * those cases where it does anything other than a memset. */ PNG_FUNCTION(void,PNGAPI png_info_init_3,(png_infopp ptr_ptr, size_t png_info_struct_size), PNG_DEPRECATED) { … } void PNGAPI png_data_freer(png_const_structrp png_ptr, png_inforp info_ptr, int freer, png_uint_32 mask) { … } void PNGAPI png_free_data(png_const_structrp png_ptr, png_inforp info_ptr, png_uint_32 mask, int num) { … } #endif /* READ || WRITE */ /* This function returns a pointer to the io_ptr associated with the user * functions. The application should free any memory associated with this * pointer before png_write_destroy() or png_read_destroy() are called. */ png_voidp PNGAPI png_get_io_ptr(png_const_structrp png_ptr) { … } #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) # ifdef PNG_STDIO_SUPPORTED /* Initialize the default input/output functions for the PNG file. If you * use your own read or write routines, you can call either png_set_read_fn() * or png_set_write_fn() instead of png_init_io(). If you have defined * PNG_NO_STDIO or otherwise disabled PNG_STDIO_SUPPORTED, you must use a * function of your own because "FILE *" isn't necessarily available. */ void PNGAPI png_init_io(png_structrp png_ptr, png_FILE_p fp) { … } # endif # ifdef PNG_SAVE_INT_32_SUPPORTED /* PNG signed integers are saved in 32-bit 2's complement format. ANSI C-90 * defines a cast of a signed integer to an unsigned integer either to preserve * the value, if it is positive, or to calculate: * * (UNSIGNED_MAX+1) + integer * * Where UNSIGNED_MAX is the appropriate maximum unsigned value, so when the * negative integral value is added the result will be an unsigned value * corresponding to the 2's complement representation. */ void PNGAPI png_save_int_32(png_bytep buf, png_int_32 i) { … } # endif # ifdef PNG_TIME_RFC1123_SUPPORTED /* Convert the supplied time into an RFC 1123 string suitable for use in * a "Creation Time" or other text-based time string. */ int PNGAPI png_convert_to_rfc1123_buffer(char out[29], png_const_timep ptime) { static const char short_months[12][4] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"}; if (out == NULL) return 0; if (ptime->year > 9999 /* RFC1123 limitation */ || ptime->month == 0 || ptime->month > 12 || ptime->day == 0 || ptime->day > 31 || ptime->hour > 23 || ptime->minute > 59 || ptime->second > 60) return 0; { size_t pos = 0; char number_buf[5] = {0, 0, 0, 0, 0}; /* enough for a four-digit year */ #define APPEND_STRING … #define APPEND_NUMBER … #define APPEND … APPEND_NUMBER(PNG_NUMBER_FORMAT_u, (unsigned)ptime->day); APPEND(' '); APPEND_STRING(short_months[(ptime->month - 1)]); APPEND(' '); APPEND_NUMBER(PNG_NUMBER_FORMAT_u, ptime->year); APPEND(' '); APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->hour); APPEND(':'); APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->minute); APPEND(':'); APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->second); APPEND_STRING(" +0000"); /* This reliably terminates the buffer */ PNG_UNUSED (pos) # undef APPEND # undef APPEND_NUMBER # undef APPEND_STRING } return 1; } # if PNG_LIBPNG_VER < 10700 /* To do: remove the following from libpng-1.7 */ /* Original API that uses a private buffer in png_struct. * Deprecated because it causes png_struct to carry a spurious temporary * buffer (png_struct::time_buffer), better to have the caller pass this in. */ png_const_charp PNGAPI png_convert_to_rfc1123(png_structrp png_ptr, png_const_timep ptime) { if (png_ptr != NULL) { /* The only failure above if png_ptr != NULL is from an invalid ptime */ if (png_convert_to_rfc1123_buffer(png_ptr->time_buffer, ptime) == 0) png_warning(png_ptr, "Ignoring invalid time value"); else return png_ptr->time_buffer; } return NULL; } # endif /* LIBPNG_VER < 10700 */ # endif /* TIME_RFC1123 */ #endif /* READ || WRITE */ png_const_charp PNGAPI png_get_copyright(png_const_structrp png_ptr) { … } /* The following return the library version as a short string in the * format 1.0.0 through 99.99.99zz. To get the version of *.h files * used with your application, print out PNG_LIBPNG_VER_STRING, which * is defined in png.h. * Note: now there is no difference between png_get_libpng_ver() and * png_get_header_ver(). Due to the version_nn_nn_nn typedef guard, * it is guaranteed that png.c uses the correct version of png.h. */ png_const_charp PNGAPI png_get_libpng_ver(png_const_structrp png_ptr) { … } png_const_charp PNGAPI png_get_header_ver(png_const_structrp png_ptr) { … } png_const_charp PNGAPI png_get_header_version(png_const_structrp png_ptr) { … } #ifdef PNG_BUILD_GRAYSCALE_PALETTE_SUPPORTED /* NOTE: this routine is not used internally! */ /* Build a grayscale palette. Palette is assumed to be 1 << bit_depth * large of png_color. This lets grayscale images be treated as * paletted. Most useful for gamma correction and simplification * of code. This API is not used internally. */ void PNGAPI png_build_grayscale_palette(int bit_depth, png_colorp palette) { int num_palette; int color_inc; int i; int v; png_debug(1, "in png_do_build_grayscale_palette"); if (palette == NULL) return; switch (bit_depth) { case 1: num_palette = 2; color_inc = 0xff; break; case 2: num_palette = 4; color_inc = 0x55; break; case 4: num_palette = 16; color_inc = 0x11; break; case 8: num_palette = 256; color_inc = 1; break; default: num_palette = 0; color_inc = 0; break; } for (i = 0, v = 0; i < num_palette; i++, v += color_inc) { palette[i].red = (png_byte)(v & 0xff); palette[i].green = (png_byte)(v & 0xff); palette[i].blue = (png_byte)(v & 0xff); } } #endif #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED int PNGAPI png_handle_as_unknown(png_const_structrp png_ptr, png_const_bytep chunk_name) { … } #if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED) ||\ defined(PNG_HANDLE_AS_UNKNOWN_SUPPORTED) int /* PRIVATE */ png_chunk_unknown_handling(png_const_structrp png_ptr, png_uint_32 chunk_name) { … } #endif /* READ_UNKNOWN_CHUNKS || HANDLE_AS_UNKNOWN */ #endif /* SET_UNKNOWN_CHUNKS */ #ifdef PNG_READ_SUPPORTED /* This function, added to libpng-1.0.6g, is untested. */ int PNGAPI png_reset_zstream(png_structrp png_ptr) { … } #endif /* READ */ /* This function was added to libpng-1.0.7 */ png_uint_32 PNGAPI png_access_version_number(void) { … } #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) /* Ensure that png_ptr->zstream.msg holds some appropriate error message string. * If it doesn't 'ret' is used to set it to something appropriate, even in cases * like Z_OK or Z_STREAM_END where the error code is apparently a success code. */ void /* PRIVATE */ png_zstream_error(png_structrp png_ptr, int ret) { … } /* png_convert_size: a PNGAPI but no longer in png.h, so deleted * at libpng 1.5.5! */ /* Added at libpng version 1.2.34 and 1.4.0 (moved from pngset.c) */ #ifdef PNG_GAMMA_SUPPORTED /* always set if COLORSPACE */ static int png_colorspace_check_gamma(png_const_structrp png_ptr, png_colorspacerp colorspace, png_fixed_point gAMA, int from) /* This is called to check a new gamma value against an existing one. The * routine returns false if the new gamma value should not be written. * * 'from' says where the new gamma value comes from: * * 0: the new gamma value is the libpng estimate for an ICC profile * 1: the new gamma value comes from a gAMA chunk * 2: the new gamma value comes from an sRGB chunk */ { … } void /* PRIVATE */ png_colorspace_set_gamma(png_const_structrp png_ptr, png_colorspacerp colorspace, png_fixed_point gAMA) { … } void /* PRIVATE */ png_colorspace_sync_info(png_const_structrp png_ptr, png_inforp info_ptr) { … } #ifdef PNG_READ_SUPPORTED void /* PRIVATE */ png_colorspace_sync(png_const_structrp png_ptr, png_inforp info_ptr) { … } #endif #endif /* GAMMA */ #ifdef PNG_COLORSPACE_SUPPORTED /* Added at libpng-1.5.5 to support read and write of true CIEXYZ values for * cHRM, as opposed to using chromaticities. These internal APIs return * non-zero on a parameter error. The X, Y and Z values are required to be * positive and less than 1.0. */ static int png_xy_from_XYZ(png_xy *xy, const png_XYZ *XYZ) { … } static int png_XYZ_from_xy(png_XYZ *XYZ, const png_xy *xy) { … } static int png_XYZ_normalize(png_XYZ *XYZ) { … } static int png_colorspace_endpoints_match(const png_xy *xy1, const png_xy *xy2, int delta) { … } /* Added in libpng-1.6.0, a different check for the validity of a set of cHRM * chunk chromaticities. Earlier checks used to simply look for the overflow * condition (where the determinant of the matrix to solve for XYZ ends up zero * because the chromaticity values are not all distinct.) Despite this it is * theoretically possible to produce chromaticities that are apparently valid * but that rapidly degrade to invalid, potentially crashing, sets because of * arithmetic inaccuracies when calculations are performed on them. The new * check is to round-trip xy -> XYZ -> xy and then check that the result is * within a small percentage of the original. */ static int png_colorspace_check_xy(png_XYZ *XYZ, const png_xy *xy) { … } /* This is the check going the other way. The XYZ is modified to normalize it * (another side-effect) and the xy chromaticities are returned. */ static int png_colorspace_check_XYZ(png_xy *xy, png_XYZ *XYZ) { … } /* Used to check for an endpoint match against sRGB */ static const png_xy sRGB_xy = …/* From ITU-R BT.709-3 */ { … }; static int png_colorspace_set_xy_and_XYZ(png_const_structrp png_ptr, png_colorspacerp colorspace, const png_xy *xy, const png_XYZ *XYZ, int preferred) { … } int /* PRIVATE */ png_colorspace_set_chromaticities(png_const_structrp png_ptr, png_colorspacerp colorspace, const png_xy *xy, int preferred) { … } int /* PRIVATE */ png_colorspace_set_endpoints(png_const_structrp png_ptr, png_colorspacerp colorspace, const png_XYZ *XYZ_in, int preferred) { … } #if defined(PNG_sRGB_SUPPORTED) || defined(PNG_iCCP_SUPPORTED) /* Error message generation */ static char png_icc_tag_char(png_uint_32 byte) { … } static void png_icc_tag_name(char *name, png_uint_32 tag) { … } static int is_ICC_signature_char(png_alloc_size_t it) { … } static int is_ICC_signature(png_alloc_size_t it) { … } static int png_icc_profile_error(png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_alloc_size_t value, png_const_charp reason) { … } #endif /* sRGB || iCCP */ #ifdef PNG_sRGB_SUPPORTED int /* PRIVATE */ png_colorspace_set_sRGB(png_const_structrp png_ptr, png_colorspacerp colorspace, int intent) { … } #endif /* sRGB */ #ifdef PNG_iCCP_SUPPORTED /* Encoded value of D50 as an ICC XYZNumber. From the ICC 2010 spec the value * is XYZ(0.9642,1.0,0.8249), which scales to: * * (63189.8112, 65536, 54060.6464) */ static const png_byte D50_nCIEXYZ[12] = …; static int /* bool */ icc_check_length(png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length) { … } #ifdef PNG_READ_iCCP_SUPPORTED int /* PRIVATE */ png_icc_check_length(png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length) { … } #endif /* READ_iCCP */ int /* PRIVATE */ png_icc_check_header(png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length, png_const_bytep profile/* first 132 bytes only */, int color_type) { … } int /* PRIVATE */ png_icc_check_tag_table(png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length, png_const_bytep profile /* header plus whole tag table */) { … } #ifdef PNG_sRGB_SUPPORTED #if PNG_sRGB_PROFILE_CHECKS >= 0 /* Information about the known ICC sRGB profiles */ static const struct { … } png_sRGB_checks[] = …; static int png_compare_ICC_profile_with_sRGB(png_const_structrp png_ptr, png_const_bytep profile, uLong adler) { … } void /* PRIVATE */ png_icc_set_sRGB(png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_bytep profile, uLong adler) { … } #endif /* PNG_sRGB_PROFILE_CHECKS >= 0 */ #endif /* sRGB */ int /* PRIVATE */ png_colorspace_set_ICC(png_const_structrp png_ptr, png_colorspacerp colorspace, png_const_charp name, png_uint_32 profile_length, png_const_bytep profile, int color_type) { … } #endif /* iCCP */ #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED void /* PRIVATE */ png_colorspace_set_rgb_coefficients(png_structrp png_ptr) { … } #endif /* READ_RGB_TO_GRAY */ #endif /* COLORSPACE */ void /* PRIVATE */ png_check_IHDR(png_const_structrp png_ptr, png_uint_32 width, png_uint_32 height, int bit_depth, int color_type, int interlace_type, int compression_type, int filter_type) { … } #if defined(PNG_sCAL_SUPPORTED) || defined(PNG_pCAL_SUPPORTED) /* ASCII to fp functions */ /* Check an ASCII formatted floating point value, see the more detailed * comments in pngpriv.h */ /* The following is used internally to preserve the sticky flags */ #define png_fp_add … #define png_fp_set … int /* PRIVATE */ png_check_fp_number(png_const_charp string, size_t size, int *statep, size_t *whereami) { int state = *statep; size_t i = *whereami; while (i < size) { int type; /* First find the type of the next character */ switch (string[i]) { case 43: type = PNG_FP_SAW_SIGN; break; case 45: type = PNG_FP_SAW_SIGN + PNG_FP_NEGATIVE; break; case 46: type = PNG_FP_SAW_DOT; break; case 48: type = PNG_FP_SAW_DIGIT; break; case 49: case 50: case 51: case 52: case 53: case 54: case 55: case 56: case 57: type = PNG_FP_SAW_DIGIT + PNG_FP_NONZERO; break; case 69: case 101: type = PNG_FP_SAW_E; break; default: goto PNG_FP_End; } /* Now deal with this type according to the current * state, the type is arranged to not overlap the * bits of the PNG_FP_STATE. */ switch ((state & PNG_FP_STATE) + (type & PNG_FP_SAW_ANY)) { case PNG_FP_INTEGER + PNG_FP_SAW_SIGN: if ((state & PNG_FP_SAW_ANY) != 0) goto PNG_FP_End; /* not a part of the number */ png_fp_add(state, type); break; case PNG_FP_INTEGER + PNG_FP_SAW_DOT: /* Ok as trailer, ok as lead of fraction. */ if ((state & PNG_FP_SAW_DOT) != 0) /* two dots */ goto PNG_FP_End; else if ((state & PNG_FP_SAW_DIGIT) != 0) /* trailing dot? */ png_fp_add(state, type); else png_fp_set(state, PNG_FP_FRACTION | type); break; case PNG_FP_INTEGER + PNG_FP_SAW_DIGIT: if ((state & PNG_FP_SAW_DOT) != 0) /* delayed fraction */ png_fp_set(state, PNG_FP_FRACTION | PNG_FP_SAW_DOT); png_fp_add(state, type | PNG_FP_WAS_VALID); break; case PNG_FP_INTEGER + PNG_FP_SAW_E: if ((state & PNG_FP_SAW_DIGIT) == 0) goto PNG_FP_End; png_fp_set(state, PNG_FP_EXPONENT); break; /* case PNG_FP_FRACTION + PNG_FP_SAW_SIGN: goto PNG_FP_End; ** no sign in fraction */ /* case PNG_FP_FRACTION + PNG_FP_SAW_DOT: goto PNG_FP_End; ** Because SAW_DOT is always set */ case PNG_FP_FRACTION + PNG_FP_SAW_DIGIT: png_fp_add(state, type | PNG_FP_WAS_VALID); break; case PNG_FP_FRACTION + PNG_FP_SAW_E: /* This is correct because the trailing '.' on an * integer is handled above - so we can only get here * with the sequence ".E" (with no preceding digits). */ if ((state & PNG_FP_SAW_DIGIT) == 0) goto PNG_FP_End; png_fp_set(state, PNG_FP_EXPONENT); break; case PNG_FP_EXPONENT + PNG_FP_SAW_SIGN: if ((state & PNG_FP_SAW_ANY) != 0) goto PNG_FP_End; /* not a part of the number */ png_fp_add(state, PNG_FP_SAW_SIGN); break; /* case PNG_FP_EXPONENT + PNG_FP_SAW_DOT: goto PNG_FP_End; */ case PNG_FP_EXPONENT + PNG_FP_SAW_DIGIT: png_fp_add(state, PNG_FP_SAW_DIGIT | PNG_FP_WAS_VALID); break; /* case PNG_FP_EXPONEXT + PNG_FP_SAW_E: goto PNG_FP_End; */ default: goto PNG_FP_End; /* I.e. break 2 */ } /* The character seems ok, continue. */ ++i; } PNG_FP_End: /* Here at the end, update the state and return the correct * return code. */ *statep = state; *whereami = i; return (state & PNG_FP_SAW_DIGIT) != 0; } /* The same but for a complete string. */ int png_check_fp_string(png_const_charp string, size_t size) { int state=0; size_t char_index=0; if (png_check_fp_number(string, size, &state, &char_index) != 0 && (char_index == size || string[char_index] == 0)) return state /* must be non-zero - see above */; return 0; /* i.e. fail */ } #endif /* pCAL || sCAL */ #ifdef PNG_sCAL_SUPPORTED # ifdef PNG_FLOATING_POINT_SUPPORTED /* Utility used below - a simple accurate power of ten from an integral * exponent. */ static double png_pow10(int power) { int recip = 0; double d = 1; /* Handle negative exponent with a reciprocal at the end because * 10 is exact whereas .1 is inexact in base 2 */ if (power < 0) { if (power < DBL_MIN_10_EXP) return 0; recip = 1; power = -power; } if (power > 0) { /* Decompose power bitwise. */ double mult = 10; do { if (power & 1) d *= mult; mult *= mult; power >>= 1; } while (power > 0); if (recip != 0) d = 1/d; } /* else power is 0 and d is 1 */ return d; } /* Function to format a floating point value in ASCII with a given * precision. */ void /* PRIVATE */ png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, size_t size, double fp, unsigned int precision) { /* We use standard functions from math.h, but not printf because * that would require stdio. The caller must supply a buffer of * sufficient size or we will png_error. The tests on size and * the space in ascii[] consumed are indicated below. */ if (precision < 1) precision = DBL_DIG; /* Enforce the limit of the implementation precision too. */ if (precision > DBL_DIG+1) precision = DBL_DIG+1; /* Basic sanity checks */ if (size >= precision+5) /* See the requirements below. */ { if (fp < 0) { fp = -fp; *ascii++ = 45; /* '-' PLUS 1 TOTAL 1 */ --size; } if (fp >= DBL_MIN && fp <= DBL_MAX) { int exp_b10; /* A base 10 exponent */ double base; /* 10^exp_b10 */ /* First extract a base 10 exponent of the number, * the calculation below rounds down when converting * from base 2 to base 10 (multiply by log10(2) - * 0.3010, but 77/256 is 0.3008, so exp_b10 needs to * be increased. Note that the arithmetic shift * performs a floor() unlike C arithmetic - using a * C multiply would break the following for negative * exponents. */ (void)frexp(fp, &exp_b10); /* exponent to base 2 */ exp_b10 = (exp_b10 * 77) >> 8; /* <= exponent to base 10 */ /* Avoid underflow here. */ base = png_pow10(exp_b10); /* May underflow */ while (base < DBL_MIN || base < fp) { /* And this may overflow. */ double test = png_pow10(exp_b10+1); if (test <= DBL_MAX) { ++exp_b10; base = test; } else break; } /* Normalize fp and correct exp_b10, after this fp is in the * range [.1,1) and exp_b10 is both the exponent and the digit * *before* which the decimal point should be inserted * (starting with 0 for the first digit). Note that this * works even if 10^exp_b10 is out of range because of the * test on DBL_MAX above. */ fp /= base; while (fp >= 1) { fp /= 10; ++exp_b10; } /* Because of the code above fp may, at this point, be * less than .1, this is ok because the code below can * handle the leading zeros this generates, so no attempt * is made to correct that here. */ { unsigned int czero, clead, cdigits; char exponent[10]; /* Allow up to two leading zeros - this will not lengthen * the number compared to using E-n. */ if (exp_b10 < 0 && exp_b10 > -3) /* PLUS 3 TOTAL 4 */ { czero = 0U-exp_b10; /* PLUS 2 digits: TOTAL 3 */ exp_b10 = 0; /* Dot added below before first output. */ } else czero = 0; /* No zeros to add */ /* Generate the digit list, stripping trailing zeros and * inserting a '.' before a digit if the exponent is 0. */ clead = czero; /* Count of leading zeros */ cdigits = 0; /* Count of digits in list. */ do { double d; fp *= 10; /* Use modf here, not floor and subtract, so that * the separation is done in one step. At the end * of the loop don't break the number into parts so * that the final digit is rounded. */ if (cdigits+czero+1 < precision+clead) fp = modf(fp, &d); else { d = floor(fp + .5); if (d > 9) { /* Rounding up to 10, handle that here. */ if (czero > 0) { --czero; d = 1; if (cdigits == 0) --clead; } else { while (cdigits > 0 && d > 9) { int ch = *--ascii; if (exp_b10 != (-1)) ++exp_b10; else if (ch == 46) { ch = *--ascii; ++size; /* Advance exp_b10 to '1', so that the * decimal point happens after the * previous digit. */ exp_b10 = 1; } --cdigits; d = ch - 47; /* I.e. 1+(ch-48) */ } /* Did we reach the beginning? If so adjust the * exponent but take into account the leading * decimal point. */ if (d > 9) /* cdigits == 0 */ { if (exp_b10 == (-1)) { /* Leading decimal point (plus zeros?), if * we lose the decimal point here it must * be reentered below. */ int ch = *--ascii; if (ch == 46) { ++size; exp_b10 = 1; } /* Else lost a leading zero, so 'exp_b10' is * still ok at (-1) */ } else ++exp_b10; /* In all cases we output a '1' */ d = 1; } } } fp = 0; /* Guarantees termination below. */ } if (d == 0) { ++czero; if (cdigits == 0) ++clead; } else { /* Included embedded zeros in the digit count. */ cdigits += czero - clead; clead = 0; while (czero > 0) { /* exp_b10 == (-1) means we just output the decimal * place - after the DP don't adjust 'exp_b10' any * more! */ if (exp_b10 != (-1)) { if (exp_b10 == 0) { *ascii++ = 46; --size; } /* PLUS 1: TOTAL 4 */ --exp_b10; } *ascii++ = 48; --czero; } if (exp_b10 != (-1)) { if (exp_b10 == 0) { *ascii++ = 46; --size; /* counted above */ } --exp_b10; } *ascii++ = (char)(48 + (int)d); ++cdigits; } } while (cdigits+czero < precision+clead && fp > DBL_MIN); /* The total output count (max) is now 4+precision */ /* Check for an exponent, if we don't need one we are * done and just need to terminate the string. At this * point, exp_b10==(-1) is effectively a flag: it got * to '-1' because of the decrement, after outputting * the decimal point above. (The exponent required is * *not* -1.) */ if (exp_b10 >= (-1) && exp_b10 <= 2) { /* The following only happens if we didn't output the * leading zeros above for negative exponent, so this * doesn't add to the digit requirement. Note that the * two zeros here can only be output if the two leading * zeros were *not* output, so this doesn't increase * the output count. */ while (exp_b10-- > 0) *ascii++ = 48; *ascii = 0; /* Total buffer requirement (including the '\0') is * 5+precision - see check at the start. */ return; } /* Here if an exponent is required, adjust size for * the digits we output but did not count. The total * digit output here so far is at most 1+precision - no * decimal point and no leading or trailing zeros have * been output. */ size -= cdigits; *ascii++ = 69; --size; /* 'E': PLUS 1 TOTAL 2+precision */ /* The following use of an unsigned temporary avoids ambiguities in * the signed arithmetic on exp_b10 and permits GCC at least to do * better optimization. */ { unsigned int uexp_b10; if (exp_b10 < 0) { *ascii++ = 45; --size; /* '-': PLUS 1 TOTAL 3+precision */ uexp_b10 = 0U-exp_b10; } else uexp_b10 = 0U+exp_b10; cdigits = 0; while (uexp_b10 > 0) { exponent[cdigits++] = (char)(48 + uexp_b10 % 10); uexp_b10 /= 10; } } /* Need another size check here for the exponent digits, so * this need not be considered above. */ if (size > cdigits) { while (cdigits > 0) *ascii++ = exponent[--cdigits]; *ascii = 0; return; } } } else if (!(fp >= DBL_MIN)) { *ascii++ = 48; /* '0' */ *ascii = 0; return; } else { *ascii++ = 105; /* 'i' */ *ascii++ = 110; /* 'n' */ *ascii++ = 102; /* 'f' */ *ascii = 0; return; } } /* Here on buffer too small. */ png_error(png_ptr, "ASCII conversion buffer too small"); } # endif /* FLOATING_POINT */ # ifdef PNG_FIXED_POINT_SUPPORTED /* Function to format a fixed point value in ASCII. */ void /* PRIVATE */ png_ascii_from_fixed(png_const_structrp png_ptr, png_charp ascii, size_t size, png_fixed_point fp) { /* Require space for 10 decimal digits, a decimal point, a minus sign and a * trailing \0, 13 characters: */ if (size > 12) { png_uint_32 num; /* Avoid overflow here on the minimum integer. */ if (fp < 0) { *ascii++ = 45; num = (png_uint_32)(-fp); } else num = (png_uint_32)fp; if (num <= 0x80000000) /* else overflowed */ { unsigned int ndigits = 0, first = 16 /* flag value */; char digits[10] = {0}; while (num) { /* Split the low digit off num: */ unsigned int tmp = num/10; num -= tmp*10; digits[ndigits++] = (char)(48 + num); /* Record the first non-zero digit, note that this is a number * starting at 1, it's not actually the array index. */ if (first == 16 && num > 0) first = ndigits; num = tmp; } if (ndigits > 0) { while (ndigits > 5) *ascii++ = digits[--ndigits]; /* The remaining digits are fractional digits, ndigits is '5' or * smaller at this point. It is certainly not zero. Check for a * non-zero fractional digit: */ if (first <= 5) { unsigned int i; *ascii++ = 46; /* decimal point */ /* ndigits may be <5 for small numbers, output leading zeros * then ndigits digits to first: */ i = 5; while (ndigits < i) { *ascii++ = 48; --i; } while (ndigits >= first) *ascii++ = digits[--ndigits]; /* Don't output the trailing zeros! */ } } else *ascii++ = 48; /* And null terminate the string: */ *ascii = 0; return; } } /* Here on buffer too small. */ png_error(png_ptr, "ASCII conversion buffer too small"); } # endif /* FIXED_POINT */ #endif /* SCAL */ #if defined(PNG_FLOATING_POINT_SUPPORTED) && \ !defined(PNG_FIXED_POINT_MACRO_SUPPORTED) && \ (defined(PNG_gAMA_SUPPORTED) || defined(PNG_cHRM_SUPPORTED) || \ defined(PNG_sCAL_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED) || \ defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)) || \ (defined(PNG_sCAL_SUPPORTED) && \ defined(PNG_FLOATING_ARITHMETIC_SUPPORTED)) png_fixed_point png_fixed(png_const_structrp png_ptr, double fp, png_const_charp text) { … } #endif #if defined(PNG_GAMMA_SUPPORTED) || defined(PNG_COLORSPACE_SUPPORTED) ||\ defined(PNG_INCH_CONVERSIONS_SUPPORTED) || defined(PNG_READ_pHYs_SUPPORTED) /* muldiv functions */ /* This API takes signed arguments and rounds the result to the nearest * integer (or, for a fixed point number - the standard argument - to * the nearest .00001). Overflow and divide by zero are signalled in * the result, a boolean - true on success, false on overflow. */ int png_muldiv(png_fixed_point_p res, png_fixed_point a, png_int_32 times, png_int_32 divisor) { … } #endif /* READ_GAMMA || INCH_CONVERSIONS */ #if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_INCH_CONVERSIONS_SUPPORTED) /* The following is for when the caller doesn't much care about the * result. */ png_fixed_point png_muldiv_warn(png_const_structrp png_ptr, png_fixed_point a, png_int_32 times, png_int_32 divisor) { … } #endif #ifdef PNG_GAMMA_SUPPORTED /* more fixed point functions for gamma */ /* Calculate a reciprocal, return 0 on div-by-zero or overflow. */ png_fixed_point png_reciprocal(png_fixed_point a) { … } /* This is the shared test on whether a gamma value is 'significant' - whether * it is worth doing gamma correction. */ int /* PRIVATE */ png_gamma_significant(png_fixed_point gamma_val) { … } #endif #ifdef PNG_READ_GAMMA_SUPPORTED #ifdef PNG_16BIT_SUPPORTED /* A local convenience routine. */ static png_fixed_point png_product2(png_fixed_point a, png_fixed_point b) { … } #endif /* 16BIT */ /* The inverse of the above. */ png_fixed_point png_reciprocal2(png_fixed_point a, png_fixed_point b) { … } #endif /* READ_GAMMA */ #ifdef PNG_READ_GAMMA_SUPPORTED /* gamma table code */ #ifndef PNG_FLOATING_ARITHMETIC_SUPPORTED /* Fixed point gamma. * * The code to calculate the tables used below can be found in the shell script * contrib/tools/intgamma.sh * * To calculate gamma this code implements fast log() and exp() calls using only * fixed point arithmetic. This code has sufficient precision for either 8-bit * or 16-bit sample values. * * The tables used here were calculated using simple 'bc' programs, but C double * precision floating point arithmetic would work fine. * * 8-bit log table * This is a table of -log(value/255)/log(2) for 'value' in the range 128 to * 255, so it's the base 2 logarithm of a normalized 8-bit floating point * mantissa. The numbers are 32-bit fractions. */ static const png_uint_32 png_8bit_l2[128] = { 4270715492U, 4222494797U, 4174646467U, 4127164793U, 4080044201U, 4033279239U, 3986864580U, 3940795015U, 3895065449U, 3849670902U, 3804606499U, 3759867474U, 3715449162U, 3671346997U, 3627556511U, 3584073329U, 3540893168U, 3498011834U, 3455425220U, 3413129301U, 3371120137U, 3329393864U, 3287946700U, 3246774933U, 3205874930U, 3165243125U, 3124876025U, 3084770202U, 3044922296U, 3005329011U, 2965987113U, 2926893432U, 2888044853U, 2849438323U, 2811070844U, 2772939474U, 2735041326U, 2697373562U, 2659933400U, 2622718104U, 2585724991U, 2548951424U, 2512394810U, 2476052606U, 2439922311U, 2404001468U, 2368287663U, 2332778523U, 2297471715U, 2262364947U, 2227455964U, 2192742551U, 2158222529U, 2123893754U, 2089754119U, 2055801552U, 2022034013U, 1988449497U, 1955046031U, 1921821672U, 1888774511U, 1855902668U, 1823204291U, 1790677560U, 1758320682U, 1726131893U, 1694109454U, 1662251657U, 1630556815U, 1599023271U, 1567649391U, 1536433567U, 1505374214U, 1474469770U, 1443718700U, 1413119487U, 1382670639U, 1352370686U, 1322218179U, 1292211689U, 1262349810U, 1232631153U, 1203054352U, 1173618059U, 1144320946U, 1115161701U, 1086139034U, 1057251672U, 1028498358U, 999877854U, 971388940U, 943030410U, 914801076U, 886699767U, 858725327U, 830876614U, 803152505U, 775551890U, 748073672U, 720716771U, 693480120U, 666362667U, 639363374U, 612481215U, 585715177U, 559064263U, 532527486U, 506103872U, 479792461U, 453592303U, 427502463U, 401522014U, 375650043U, 349885648U, 324227938U, 298676034U, 273229066U, 247886176U, 222646516U, 197509248U, 172473545U, 147538590U, 122703574U, 97967701U, 73330182U, 48790236U, 24347096U, 0U #if 0 /* The following are the values for 16-bit tables - these work fine for the * 8-bit conversions but produce very slightly larger errors in the 16-bit * log (about 1.2 as opposed to 0.7 absolute error in the final value). To * use these all the shifts below must be adjusted appropriately. */ 65166, 64430, 63700, 62976, 62257, 61543, 60835, 60132, 59434, 58741, 58054, 57371, 56693, 56020, 55352, 54689, 54030, 53375, 52726, 52080, 51439, 50803, 50170, 49542, 48918, 48298, 47682, 47070, 46462, 45858, 45257, 44661, 44068, 43479, 42894, 42312, 41733, 41159, 40587, 40020, 39455, 38894, 38336, 37782, 37230, 36682, 36137, 35595, 35057, 34521, 33988, 33459, 32932, 32408, 31887, 31369, 30854, 30341, 29832, 29325, 28820, 28319, 27820, 27324, 26830, 26339, 25850, 25364, 24880, 24399, 23920, 23444, 22970, 22499, 22029, 21562, 21098, 20636, 20175, 19718, 19262, 18808, 18357, 17908, 17461, 17016, 16573, 16132, 15694, 15257, 14822, 14390, 13959, 13530, 13103, 12678, 12255, 11834, 11415, 10997, 10582, 10168, 9756, 9346, 8937, 8531, 8126, 7723, 7321, 6921, 6523, 6127, 5732, 5339, 4947, 4557, 4169, 3782, 3397, 3014, 2632, 2251, 1872, 1495, 1119, 744, 372 #endif }; static png_int_32 png_log8bit(unsigned int x) { unsigned int lg2 = 0; /* Each time 'x' is multiplied by 2, 1 must be subtracted off the final log, * because the log is actually negate that means adding 1. The final * returned value thus has the range 0 (for 255 input) to 7.994 (for 1 * input), return -1 for the overflow (log 0) case, - so the result is * always at most 19 bits. */ if ((x &= 0xff) == 0) return -1; if ((x & 0xf0) == 0) lg2 = 4, x <<= 4; if ((x & 0xc0) == 0) lg2 += 2, x <<= 2; if ((x & 0x80) == 0) lg2 += 1, x <<= 1; /* result is at most 19 bits, so this cast is safe: */ return (png_int_32)((lg2 << 16) + ((png_8bit_l2[x-128]+32768)>>16)); } /* The above gives exact (to 16 binary places) log2 values for 8-bit images, * for 16-bit images we use the most significant 8 bits of the 16-bit value to * get an approximation then multiply the approximation by a correction factor * determined by the remaining up to 8 bits. This requires an additional step * in the 16-bit case. * * We want log2(value/65535), we have log2(v'/255), where: * * value = v' * 256 + v'' * = v' * f * * So f is value/v', which is equal to (256+v''/v') since v' is in the range 128 * to 255 and v'' is in the range 0 to 255 f will be in the range 256 to less * than 258. The final factor also needs to correct for the fact that our 8-bit * value is scaled by 255, whereas the 16-bit values must be scaled by 65535. * * This gives a final formula using a calculated value 'x' which is value/v' and * scaling by 65536 to match the above table: * * log2(x/257) * 65536 * * Since these numbers are so close to '1' we can use simple linear * interpolation between the two end values 256/257 (result -368.61) and 258/257 * (result 367.179). The values used below are scaled by a further 64 to give * 16-bit precision in the interpolation: * * Start (256): -23591 * Zero (257): 0 * End (258): 23499 */ #ifdef PNG_16BIT_SUPPORTED static png_int_32 png_log16bit(png_uint_32 x) { unsigned int lg2 = 0; /* As above, but now the input has 16 bits. */ if ((x &= 0xffff) == 0) return -1; if ((x & 0xff00) == 0) lg2 = 8, x <<= 8; if ((x & 0xf000) == 0) lg2 += 4, x <<= 4; if ((x & 0xc000) == 0) lg2 += 2, x <<= 2; if ((x & 0x8000) == 0) lg2 += 1, x <<= 1; /* Calculate the base logarithm from the top 8 bits as a 28-bit fractional * value. */ lg2 <<= 28; lg2 += (png_8bit_l2[(x>>8)-128]+8) >> 4; /* Now we need to interpolate the factor, this requires a division by the top * 8 bits. Do this with maximum precision. */ x = ((x << 16) + (x >> 9)) / (x >> 8); /* Since we divided by the top 8 bits of 'x' there will be a '1' at 1<<24, * the value at 1<<16 (ignoring this) will be 0 or 1; this gives us exactly * 16 bits to interpolate to get the low bits of the result. Round the * answer. Note that the end point values are scaled by 64 to retain overall * precision and that 'lg2' is current scaled by an extra 12 bits, so adjust * the overall scaling by 6-12. Round at every step. */ x -= 1U << 24; if (x <= 65536U) /* <= '257' */ lg2 += ((23591U * (65536U-x)) + (1U << (16+6-12-1))) >> (16+6-12); else lg2 -= ((23499U * (x-65536U)) + (1U << (16+6-12-1))) >> (16+6-12); /* Safe, because the result can't have more than 20 bits: */ return (png_int_32)((lg2 + 2048) >> 12); } #endif /* 16BIT */ /* The 'exp()' case must invert the above, taking a 20-bit fixed point * logarithmic value and returning a 16 or 8-bit number as appropriate. In * each case only the low 16 bits are relevant - the fraction - since the * integer bits (the top 4) simply determine a shift. * * The worst case is the 16-bit distinction between 65535 and 65534. This * requires perhaps spurious accuracy in the decoding of the logarithm to * distinguish log2(65535/65534.5) - 10^-5 or 17 bits. There is little chance * of getting this accuracy in practice. * * To deal with this the following exp() function works out the exponent of the * fractional part of the logarithm by using an accurate 32-bit value from the * top four fractional bits then multiplying in the remaining bits. */ static const png_uint_32 png_32bit_exp[16] = { /* NOTE: the first entry is deliberately set to the maximum 32-bit value. */ 4294967295U, 4112874773U, 3938502376U, 3771522796U, 3611622603U, 3458501653U, 3311872529U, 3171459999U, 3037000500U, 2908241642U, 2784941738U, 2666869345U, 2553802834U, 2445529972U, 2341847524U, 2242560872U }; /* Adjustment table; provided to explain the numbers in the code below. */ #if 0 for (i=11;i>=0;--i){ print i, " ", (1 - e(-(2^i)/65536*l(2))) * 2^(32-i), "\n"} 11 44937.64284865548751208448 10 45180.98734845585101160448 9 45303.31936980687359311872 8 45364.65110595323018870784 7 45395.35850361789624614912 6 45410.72259715102037508096 5 45418.40724413220722311168 4 45422.25021786898173001728 3 45424.17186732298419044352 2 45425.13273269940811464704 1 45425.61317555035558641664 0 45425.85339951654943850496 #endif static png_uint_32 png_exp(png_fixed_point x) { if (x > 0 && x <= 0xfffff) /* Else overflow or zero (underflow) */ { /* Obtain a 4-bit approximation */ png_uint_32 e = png_32bit_exp[(x >> 12) & 0x0f]; /* Incorporate the low 12 bits - these decrease the returned value by * multiplying by a number less than 1 if the bit is set. The multiplier * is determined by the above table and the shift. Notice that the values * converge on 45426 and this is used to allow linear interpolation of the * low bits. */ if (x & 0x800) e -= (((e >> 16) * 44938U) + 16U) >> 5; if (x & 0x400) e -= (((e >> 16) * 45181U) + 32U) >> 6; if (x & 0x200) e -= (((e >> 16) * 45303U) + 64U) >> 7; if (x & 0x100) e -= (((e >> 16) * 45365U) + 128U) >> 8; if (x & 0x080) e -= (((e >> 16) * 45395U) + 256U) >> 9; if (x & 0x040) e -= (((e >> 16) * 45410U) + 512U) >> 10; /* And handle the low 6 bits in a single block. */ e -= (((e >> 16) * 355U * (x & 0x3fU)) + 256U) >> 9; /* Handle the upper bits of x. */ e >>= x >> 16; return e; } /* Check for overflow */ if (x <= 0) return png_32bit_exp[0]; /* Else underflow */ return 0; } static png_byte png_exp8bit(png_fixed_point lg2) { /* Get a 32-bit value: */ png_uint_32 x = png_exp(lg2); /* Convert the 32-bit value to 0..255 by multiplying by 256-1. Note that the * second, rounding, step can't overflow because of the first, subtraction, * step. */ x -= x >> 8; return (png_byte)(((x + 0x7fffffU) >> 24) & 0xff); } #ifdef PNG_16BIT_SUPPORTED static png_uint_16 png_exp16bit(png_fixed_point lg2) { /* Get a 32-bit value: */ png_uint_32 x = png_exp(lg2); /* Convert the 32-bit value to 0..65535 by multiplying by 65536-1: */ x -= x >> 16; return (png_uint_16)((x + 32767U) >> 16); } #endif /* 16BIT */ #endif /* FLOATING_ARITHMETIC */ png_byte png_gamma_8bit_correct(unsigned int value, png_fixed_point gamma_val) { … } #ifdef PNG_16BIT_SUPPORTED png_uint_16 png_gamma_16bit_correct(unsigned int value, png_fixed_point gamma_val) { … } #endif /* 16BIT */ /* This does the right thing based on the bit_depth field of the * png_struct, interpreting values as 8-bit or 16-bit. While the result * is nominally a 16-bit value if bit depth is 8 then the result is * 8-bit (as are the arguments.) */ png_uint_16 /* PRIVATE */ png_gamma_correct(png_structrp png_ptr, unsigned int value, png_fixed_point gamma_val) { … } #ifdef PNG_16BIT_SUPPORTED /* Internal function to build a single 16-bit table - the table consists of * 'num' 256 entry subtables, where 'num' is determined by 'shift' - the amount * to shift the input values right (or 16-number_of_signifiant_bits). * * The caller is responsible for ensuring that the table gets cleaned up on * png_error (i.e. if one of the mallocs below fails) - i.e. the *table argument * should be somewhere that will be cleaned. */ static void png_build_16bit_table(png_structrp png_ptr, png_uint_16pp *ptable, unsigned int shift, png_fixed_point gamma_val) { … } /* NOTE: this function expects the *inverse* of the overall gamma transformation * required. */ static void png_build_16to8_table(png_structrp png_ptr, png_uint_16pp *ptable, unsigned int shift, png_fixed_point gamma_val) { … } #endif /* 16BIT */ /* Build a single 8-bit table: same as the 16-bit case but much simpler (and * typically much faster). Note that libpng currently does no sBIT processing * (apparently contrary to the spec) so a 256-entry table is always generated. */ static void png_build_8bit_table(png_structrp png_ptr, png_bytepp ptable, png_fixed_point gamma_val) { … } /* Used from png_read_destroy and below to release the memory used by the gamma * tables. */ void /* PRIVATE */ png_destroy_gamma_table(png_structrp png_ptr) { … } /* We build the 8- or 16-bit gamma tables here. Note that for 16-bit * tables, we don't make a full table if we are reducing to 8-bit in * the future. Note also how the gamma_16 tables are segmented so that * we don't need to allocate > 64K chunks for a full 16-bit table. */ void /* PRIVATE */ png_build_gamma_table(png_structrp png_ptr, int bit_depth) { … } #endif /* READ_GAMMA */ /* HARDWARE OR SOFTWARE OPTION SUPPORT */ #ifdef PNG_SET_OPTION_SUPPORTED int PNGAPI png_set_option(png_structrp png_ptr, int option, int onoff) { … } #endif /* sRGB support */ #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) ||\ defined(PNG_SIMPLIFIED_WRITE_SUPPORTED) /* sRGB conversion tables; these are machine generated with the code in * contrib/tools/makesRGB.c. The actual sRGB transfer curve defined in the * specification (see the article at https://en.wikipedia.org/wiki/SRGB) * is used, not the gamma=1/2.2 approximation use elsewhere in libpng. * The sRGB to linear table is exact (to the nearest 16-bit linear fraction). * The inverse (linear to sRGB) table has accuracies as follows: * * For all possible (255*65535+1) input values: * * error: -0.515566 - 0.625971, 79441 (0.475369%) of readings inexact * * For the input values corresponding to the 65536 16-bit values: * * error: -0.513727 - 0.607759, 308 (0.469978%) of readings inexact * * In all cases the inexact readings are only off by one. */ #ifdef PNG_SIMPLIFIED_READ_SUPPORTED /* The convert-to-sRGB table is only currently required for read. */ const png_uint_16 png_sRGB_table[256] = …; #endif /* SIMPLIFIED_READ */ /* The base/delta tables are required for both read and write (but currently * only the simplified versions.) */ const png_uint_16 png_sRGB_base[512] = …; const png_byte png_sRGB_delta[512] = …; #endif /* SIMPLIFIED READ/WRITE sRGB support */ /* SIMPLIFIED READ/WRITE SUPPORT */ #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) ||\ defined(PNG_SIMPLIFIED_WRITE_SUPPORTED) static int png_image_free_function(png_voidp argument) { … } void PNGAPI png_image_free(png_imagep image) { … } int /* PRIVATE */ png_image_error(png_imagep image, png_const_charp error_message) { … } #endif /* SIMPLIFIED READ/WRITE */ #endif /* READ || WRITE */
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