mirror of
https://git.do.srb2.org/STJr/SRB2.git
synced 2024-12-28 05:30:47 +00:00
110 lines
2.9 KiB
Bash
110 lines
2.9 KiB
Bash
#!/bin/sh
|
|
#
|
|
# intgamma.sh
|
|
#
|
|
# Last changed in libpng 1.6.0 [February 14, 2013]
|
|
#
|
|
# COPYRIGHT: Written by John Cunningham Bowler, 2013.
|
|
# To the extent possible under law, the author has waived all copyright and
|
|
# related or neighboring rights to this work. This work is published from:
|
|
# United States.
|
|
#
|
|
# Shell script to generate png.c 8-bit and 16-bit log tables (see the code in
|
|
# png.c for details).
|
|
#
|
|
# This script uses the "bc" arbitrary precision calculator to calculate 32-bit
|
|
# fixed point values of logarithms appropriate to finding the log of an 8-bit
|
|
# (0..255) value and a similar table for the exponent calculation.
|
|
#
|
|
# "bc" must be on the path when the script is executed, and the math library
|
|
# (-lm) must be available
|
|
#
|
|
# function to print out a list of numbers as integers; the function truncates
|
|
# the integers which must be one-per-line
|
|
function print(){
|
|
awk 'BEGIN{
|
|
str = ""
|
|
}
|
|
{
|
|
sub("\\.[0-9]*$", "")
|
|
if ($0 == "")
|
|
$0 = "0"
|
|
|
|
if (str == "")
|
|
t = " " $0 "U"
|
|
else
|
|
t = str ", " $0 "U"
|
|
|
|
if (length(t) >= 80) {
|
|
print str ","
|
|
str = " " $0 "U"
|
|
} else
|
|
str = t
|
|
}
|
|
END{
|
|
print str
|
|
}'
|
|
}
|
|
#
|
|
# The logarithm table.
|
|
cat <<END
|
|
/* 8-bit log table: png_8bit_l2[128]
|
|
* 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] =
|
|
{
|
|
END
|
|
#
|
|
bc -lqws <<END | print
|
|
f=65536*65536/l(2)
|
|
for (i=128;i<256;++i) { .5 - l(i/255)*f; }
|
|
END
|
|
echo '};'
|
|
echo
|
|
#
|
|
# The exponent table.
|
|
cat <<END
|
|
/* 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
|
|
* frational 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] =
|
|
{
|
|
END
|
|
#
|
|
bc -lqws <<END | print
|
|
f=l(2)/16
|
|
for (i=0;i<16;++i) {
|
|
x = .5 + e(-i*f)*2^32;
|
|
if (x >= 2^32) x = 2^32-1;
|
|
x;
|
|
}
|
|
END
|
|
echo '};'
|
|
echo
|
|
#
|
|
# And the table of adjustment values.
|
|
cat <<END
|
|
/* Adjustment table; provided to explain the numbers in the code below. */
|
|
#if 0
|
|
END
|
|
bc -lqws <<END | awk '{ printf "%5d %s\n", 12-NR, $0 }'
|
|
for (i=11;i>=0;--i){
|
|
(1 - e(-(2^i)/65536*l(2))) * 2^(32-i)
|
|
}
|
|
END
|
|
echo '#endif'
|