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https://git.code.sf.net/p/libpng/code.git
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f6036c0aeb
Rename contrib/tools/chkfmt to contrib/tools/chkfmt.sh; refactor: * Increase the max line length for contrib/**/*.[ch] from 96 to 100. * Set the max line length for ci_*.sh to 100. * Use `basename $0` instead of the hard-coded script name. * Update comments. Remove contrib/tools/reindent. For automated code formatting, including indentation, we need a robust solution. Add an empty line after the hashbang line in all scripts. Remove the "last changed" version info from comment headers. (The version control system maintains this information automatically.)
109 lines
2.8 KiB
Bash
Executable File
109 lines
2.8 KiB
Bash
Executable File
#!/bin/sh
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# intgamma.sh
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#
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# COPYRIGHT: Written by John Cunningham Bowler, 2013.
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# To the extent possible under law, the author has waived all copyright and
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# related or neighboring rights to this work. The author published this work
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# from the United States.
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#
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# Shell script to generate png.c 8-bit and 16-bit log tables (see the code in
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# png.c for details).
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#
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# This script uses the "bc" arbitrary precision calculator to calculate 32-bit
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# fixed point values of logarithms appropriate to finding the log of an 8-bit
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# (0..255) value and a similar table for the exponent calculation.
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#
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# "bc" must be on the path when the script is executed, and the math library
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# (-lm) must be available.
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# Function to print out a list of numbers as integers; the function truncates
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# the integers which must be one-per-line.
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function print(){
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awk 'BEGIN{
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str = ""
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}
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{
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sub("\\.[0-9]*$", "")
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if ($0 == "")
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$0 = "0"
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if (str == "")
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t = " " $0 "U"
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else
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t = str ", " $0 "U"
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if (length(t) >= 80) {
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print str ","
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str = " " $0 "U"
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} else
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str = t
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}
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END{
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print str
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}'
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}
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#
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# The logarithm table.
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cat <<END
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/* 8-bit log table: png_8bit_l2[128]
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* This is a table of -log(value/255)/log(2) for 'value' in the range 128 to
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* 255, so it's the base 2 logarithm of a normalized 8-bit floating point
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* mantissa. The numbers are 32-bit fractions.
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*/
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static const png_uint_32
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png_8bit_l2[128] =
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{
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END
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#
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bc -lqws <<END | print
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f=65536*65536/l(2)
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for (i=128;i<256;++i) { .5 - l(i/255)*f; }
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END
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echo '};'
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echo
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#
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# The exponent table.
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cat <<END
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/* The 'exp()' case must invert the above, taking a 20-bit fixed point
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* logarithmic value and returning a 16 or 8-bit number as appropriate. In
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* each case only the low 16 bits are relevant - the fraction - since the
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* integer bits (the top 4) simply determine a shift.
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*
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* The worst case is the 16-bit distinction between 65535 and 65534; this
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* requires perhaps spurious accuracy in the decoding of the logarithm to
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* distinguish log2(65535/65534.5) - 10^-5 or 17 bits. There is little chance
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* of getting this accuracy in practice.
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*
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* To deal with this the following exp() function works out the exponent of the
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* frational part of the logarithm by using an accurate 32-bit value from the
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* top four fractional bits then multiplying in the remaining bits.
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*/
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static const png_uint_32
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png_32bit_exp[16] =
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{
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END
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#
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bc -lqws <<END | print
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f=l(2)/16
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for (i=0;i<16;++i) {
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x = .5 + e(-i*f)*2^32;
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if (x >= 2^32) x = 2^32-1;
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x;
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}
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END
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echo '};'
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echo
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#
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# And the table of adjustment values.
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cat <<END
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/* Adjustment table; provided to explain the numbers in the code below. */
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#if 0
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END
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bc -lqws <<END | awk '{ printf "%5d %s\n", 12-NR, $0 }'
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for (i=11;i>=0;--i){
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(1 - e(-(2^i)/65536*l(2))) * 2^(32-i)
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}
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END
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echo '#endif'
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