kc3-lang/libpng/contrib/tools/intgamma.sh

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• Hash : 9f9f8d8e
  Author :
  Date : 2023-03-19T13:55:25
  

  Fix bashisms
  
  makepngs.sh relies on a Bash feature in one of its case statements,
  ";;&"; this should be made explicit in the shebang.
  
  intgamma.sh declares a function in a manner which may fail in non-Bash
  sh implementations, this patch uses the correct syntax.
  
  Based on a patch by Roflcopter4:
  https://github.com/joncampbell123/dosbox-x/pull/3850
  
  Signed-off-by: Stephen Kitt <steve@sk2.org>
  

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• contrib/tools/intgamma.sh

• #!/bin/sh
  
  # intgamma.sh
  #
  # 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.  The author published this work
  # from the 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.
  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'
  

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