[devel] Consistently use "n-bit", not "n bit" in comments.

This commit is contained in:
Glenn Randers-Pehrson
2011-05-17 06:49:32 -05:00
parent 1921e6db90
commit 55fbff358a
3 changed files with 32 additions and 32 deletions

54
png.c
View File

@@ -1791,16 +1791,16 @@ png_64bit_product (long v1, long v2, unsigned long *hi_product,
/* Fixed point gamma. /* Fixed point gamma.
* *
* To calculate gamma this code implements fast log() and exp() calls using only * To calculate gamma this code implements fast log() and exp() calls using only
* fixed point arithmetic. This code has sufficient precision for either 8 or * fixed point arithmetic. This code has sufficient precision for either 8-bit
* 16 bit sample values. * or 16-bit sample values.
* *
* The tables used here were calculated using simple 'bc' programs, but C double * The tables used here were calculated using simple 'bc' programs, but C double
* precision floating point arithmetic would work fine. The programs are given * precision floating point arithmetic would work fine. The programs are given
* at the head of each table. * at the head of each table.
* *
* 8 bit log table * 8-bit log table
* This is a table of -log(value/255)/log(2) for 'value' in the range 128 to * 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 * 255, so it's the base 2 logarithm of a normalized 8-bit floating point
* mantissa. The numbers are 32 bit fractions. * mantissa. The numbers are 32 bit fractions.
*/ */
static png_uint_32 static png_uint_32
@@ -1832,8 +1832,8 @@ png_8bit_l2[128] =
172473545U, 147538590U, 122703574U, 97967701U, 73330182U, 48790236U, 172473545U, 147538590U, 122703574U, 97967701U, 73330182U, 48790236U,
24347096U, 0U 24347096U, 0U
#if 0 #if 0
/* The following are the values for 16 bit tables - these work fine for the 8 /* 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 * 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 * (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. * these all the shifts below must be adjusted appropriately.
*/ */
@@ -1878,11 +1878,11 @@ png_log8bit(unsigned int x)
return (png_int_32)((lg2 << 16) + ((png_8bit_l2[x-128]+32768)>>16)); 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, /* 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 * 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 * get an approximation then multiply the approximation by a correction factor
* determined by the remaining up to 8 bits. This requires an additional step * determined by the remaining up to 8 bits. This requires an additional step
* in the 16 bit case. * in the 16-bit case.
* *
* We want log2(value/65535), we have log2(v'/255), where: * We want log2(value/65535), we have log2(v'/255), where:
* *
@@ -1891,8 +1891,8 @@ png_log8bit(unsigned int x)
* *
* So f is value/v', which is equal to (256+v''/v') since v' is in the range 128 * 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 * 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 * 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. * 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 * This gives a final formula using a calculated value 'x' which is value/v' and
* scaling by 65536 to match the above table: * scaling by 65536 to match the above table:
@@ -1902,7 +1902,7 @@ png_log8bit(unsigned int x)
* Since these numbers are so close to '1' we can use simple linear * 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 * 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 * (result 367.179). The values used below are scaled by a further 64 to give
* 16 bit precision in the interpolation: * 16-bit precision in the interpolation:
* *
* Start (256): -23591 * Start (256): -23591
* Zero (257): 0 * Zero (257): 0
@@ -1960,11 +1960,11 @@ png_log16bit(png_uint_32 x)
} }
/* The 'exp()' case must invert the above, taking a 20 bit fixed point /* 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 * 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 * each case only the low 16 bits are relevant - the fraction - since the
* integer bits (the top 4) simply determine a shift. * integer bits (the top 4) simply determine a shift.
* *
* The worst case is the 16 bit distinction between 65535 and 65534, this * The worst case is the 16-bit distinction between 65535 and 65534, this
* requires perhaps spurious accuracty in the decoding of the logarithm to * requires perhaps spurious accuracty in the decoding of the logarithm to
* distinguish log2(65535/65534.5) - 10^-5 or 17 bits. There is little chance * distinguish log2(65535/65534.5) - 10^-5 or 17 bits. There is little chance
* of getting this accuracy in practice. * of getting this accuracy in practice.
@@ -2123,9 +2123,9 @@ png_gamma_16bit_correct(unsigned int value, png_fixed_point gamma_val)
} }
/* This does the right thing based on the bit_depth field of the /* This does the right thing based on the bit_depth field of the
* png_struct, interpreting values as 8 or 16 bit. While the result * 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 * is nominally a 16-bit value if bit depth is 8 then the result is
* 8 bit (as are the arguments.) * 8-bit (as are the arguments.)
*/ */
png_uint_16 /* PRIVATE */ png_uint_16 /* PRIVATE */
png_gamma_correct(png_structp png_ptr, unsigned int value, png_gamma_correct(png_structp png_ptr, unsigned int value,
@@ -2148,7 +2148,7 @@ png_gamma_significant(png_fixed_point gamma_val)
gamma_val > PNG_FP_1 + PNG_GAMMA_THRESHOLD_FIXED; gamma_val > PNG_FP_1 + PNG_GAMMA_THRESHOLD_FIXED;
} }
/* Internal function to build a single 16 bit table - the table consists of /* 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 * 'num' 256 entry subtables, where 'num' is determined by 'shift' - the amount
* to shift the input values right (or 16-number_of_signifiant_bits). * to shift the input values right (or 16-number_of_signifiant_bits).
* *
@@ -2175,7 +2175,7 @@ png_build_16bit_table(png_structp png_ptr, png_uint_16pp *ptable,
(png_uint_16p)png_malloc(png_ptr, 256 * png_sizeof(png_uint_16)); (png_uint_16p)png_malloc(png_ptr, 256 * png_sizeof(png_uint_16));
/* The 'threshold' test is repeated here because it can arise for one of /* The 'threshold' test is repeated here because it can arise for one of
* the 16 bit tables even if the others don't hit it. * the 16-bit tables even if the others don't hit it.
*/ */
if (png_gamma_significant(gamma_val)) if (png_gamma_significant(gamma_val))
{ {
@@ -2237,7 +2237,7 @@ png_build_16to8_table(png_structp png_ptr, png_uint_16pp *ptable,
(png_uint_16pp)png_calloc(png_ptr, num * png_sizeof(png_uint_16p)); (png_uint_16pp)png_calloc(png_ptr, num * png_sizeof(png_uint_16p));
/* 'num' is the number of tables and also the number of low bits of low /* 'num' is the number of tables and also the number of low bits of low
* bits of the input 16 bit value used to select a table. Each table is * bits of the input 16-bit value used to select a table. Each table is
* itself index by the high 8 bits of the value. * itself index by the high 8 bits of the value.
*/ */
for (i = 0; i < num; i++) for (i = 0; i < num; i++)
@@ -2255,16 +2255,16 @@ png_build_16to8_table(png_structp png_ptr, png_uint_16pp *ptable,
* value. * value.
* *
* The boundary values are 0.5,1.5..253.5,254.5. Since these are 9 bit * The boundary values are 0.5,1.5..253.5,254.5. Since these are 9 bit
* values the code below uses a 16 bit value in i; the values start at * values the code below uses a 16-bit value in i; the values start at
* 128.5 (for 0.5) and step by 257, for a total of 254 values (the last * 128.5 (for 0.5) and step by 257, for a total of 254 values (the last
* entries are filled with 255). Start i at 128 and fill all 'last' * entries are filled with 255). Start i at 128 and fill all 'last'
* table entries <= 'max' * table entries <= 'max'
*/ */
last = 0; last = 0;
for (i = 0; i < 255; ++i) /* 8 bit output value */ for (i = 0; i < 255; ++i) /* 8-bit output value */
{ {
/* Find the corresponding maximum input value */ /* Find the corresponding maximum input value */
png_uint_16 out = (png_uint_16)(i * 257U); /* 16 bit output value */ png_uint_16 out = (png_uint_16)(i * 257U); /* 16-bit output value */
/* Find the boundary value in 16 bits: */ /* Find the boundary value in 16 bits: */
png_uint_32 bound = png_gamma_16bit_correct(out+128U, gamma_val); png_uint_32 bound = png_gamma_16bit_correct(out+128U, gamma_val);
@@ -2287,7 +2287,7 @@ png_build_16to8_table(png_structp png_ptr, png_uint_16pp *ptable,
} }
} }
/* Build a single 8 bit table: same as the 16 bit case but much simpler (and /* 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 * typically much faster). Note that libpng currently does no sBIT processing
* (apparently contrary to the spec) so a 256 entry table is always generated. * (apparently contrary to the spec) so a 256 entry table is always generated.
*/ */
@@ -2352,7 +2352,7 @@ png_build_gamma_table(png_structp png_ptr, int bit_depth)
else else
sig_bit = png_ptr->sig_bit.gray; sig_bit = png_ptr->sig_bit.gray;
/* 16 bit gamma code uses this equation: /* 16-bit gamma code uses this equation:
* *
* ov = table[(iv & 0xff) >> gamma_shift][iv >> 8] * ov = table[(iv & 0xff) >> gamma_shift][iv >> 8]
* *
@@ -2367,7 +2367,7 @@ png_build_gamma_table(png_structp png_ptr, int bit_depth)
* *
* So the table 'n' corresponds to all those 'iv' of: * So the table 'n' corresponds to all those 'iv' of:
* *
* <all high 8 bit values><n << gamma_shift>..<(n+1 << gamma_shift)-1> * <all high 8-bit values><n << gamma_shift>..<(n+1 << gamma_shift)-1>
* *
*/ */
if (sig_bit > 0 && sig_bit < 16U) if (sig_bit > 0 && sig_bit < 16U)
@@ -2394,7 +2394,7 @@ png_build_gamma_table(png_structp png_ptr, int bit_depth)
#ifdef PNG_16BIT_SUPPORTED #ifdef PNG_16BIT_SUPPORTED
/* NOTE: prior to 1.5.3 this test used to include PNG_BACKGROUND (now /* NOTE: prior to 1.5.3 this test used to include PNG_BACKGROUND (now
* PNG_COMPOSE). This effectively smashed the background calculation for * PNG_COMPOSE). This effectively smashed the background calculation for
* 16 bit output because the 8 bit table assumes the result will be reduced * 16-bit output because the 8-bit table assumes the result will be reduced
* to 8 bits. * to 8 bits.
*/ */
if (png_ptr->transformations & PNG_16_TO_8) if (png_ptr->transformations & PNG_16_TO_8)

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@@ -1287,7 +1287,7 @@ png_read_png(png_structp png_ptr, png_infop info_ptr,
/* -------------- image transformations start here ------------------- */ /* -------------- image transformations start here ------------------- */
#ifdef PNG_READ_16_TO_8_SUPPORTED #ifdef PNG_READ_16_TO_8_SUPPORTED
/* Tell libpng to strip 16 bit/color files down to 8 bits per color. /* Tell libpng to strip 16-bit/color files down to 8 bits per color.
*/ */
if (transforms & PNG_TRANSFORM_STRIP_16) if (transforms & PNG_TRANSFORM_STRIP_16)
png_set_strip_16(png_ptr); png_set_strip_16(png_ptr);
@@ -1368,7 +1368,7 @@ png_read_png(png_structp png_ptr, png_infop info_ptr,
#endif #endif
#ifdef PNG_READ_SWAP_SUPPORTED #ifdef PNG_READ_SWAP_SUPPORTED
/* Swap bytes of 16 bit files to least significant byte first */ /* Swap bytes of 16-bit files to least significant byte first */
if (transforms & PNG_TRANSFORM_SWAP_ENDIAN) if (transforms & PNG_TRANSFORM_SWAP_ENDIAN)
png_set_swap(png_ptr); png_set_swap(png_ptr);
#endif #endif

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@@ -133,7 +133,7 @@ png_set_background(png_structp png_ptr,
#endif /* READ_BACKGROUND */ #endif /* READ_BACKGROUND */
#ifdef PNG_READ_16_TO_8_SUPPORTED #ifdef PNG_READ_16_TO_8_SUPPORTED
/* Strip 16 bit depth files to 8 bit depth */ /* Strip 16-bit depth files to 8-bit depth */
void PNGAPI void PNGAPI
png_set_strip_16(png_structp png_ptr) png_set_strip_16(png_structp png_ptr)
{ {
@@ -342,7 +342,7 @@ png_set_alpha_mode(png_structp png_ptr, int mode, double output_gamma)
#endif #endif
#ifdef PNG_READ_QUANTIZE_SUPPORTED #ifdef PNG_READ_QUANTIZE_SUPPORTED
/* Dither file to 8 bit. Supply a palette, the current number /* Dither file to 8-bit. Supply a palette, the current number
* of elements in the palette, the maximum number of elements * of elements in the palette, the maximum number of elements
* allowed, and a histogram if possible. If the current number * allowed, and a histogram if possible. If the current number
* of colors is greater then the maximum number, the palette will be * of colors is greater then the maximum number, the palette will be
@@ -872,7 +872,7 @@ png_set_tRNS_to_alpha(png_structp png_ptr)
#endif /* defined(PNG_READ_EXPAND_SUPPORTED) */ #endif /* defined(PNG_READ_EXPAND_SUPPORTED) */
#ifdef PNG_READ_EXPAND_16_SUPPORTED #ifdef PNG_READ_EXPAND_16_SUPPORTED
/* Expand to 16 bit channels, expand the tRNS chunk too (because otherwise /* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
* it may not work correctly.) * it may not work correctly.)
*/ */
void PNGAPI void PNGAPI