godot/thirdparty/libpng/png.c

/* 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)
{ … }

#    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)
{ … }
#    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)
{ … }
#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(state, flags) …
#define png_fp_set(state, value) …

int /* PRIVATE */
png_check_fp_number(png_const_charp string, size_t size, int *statep,
    size_t *whereami)
{ … }


/* The same but for a complete string. */
int
png_check_fp_string(png_const_charp string, size_t size)
{ … }
#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)
{ … }

/* 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)
{ … }
#  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)
{ … }
#   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 */