source/texk/web2c/lib/zround.c

   1 /* zround.c: round R to the nearest whole number.  This is supposed to
   2    implement the predefined Pascal round function.  Public domain. */
   3
   4 #include <w2c/config.h>
   5 #include "lib.h"
   6
   7 integer
   8 zround (double r)
   9 {
  10   integer i;
  11
  12   /* R can be outside the range of an integer if glue is stretching or
  13      shrinking a lot.  We can't do any better than returning the largest
  14      or smallest integer possible in that case.  It doesn't seem to make
  15      any practical difference.  Here is a sample input file which
  16      demonstrates the problem, from phil@cs.arizona.edu:
  17         \documentstyle{article}
  18         \begin{document}
  19         \begin{flushleft}
  20         $\hbox{} $\hfill
  21         \filbreak
  22         \eject
  23
  24      djb@silverton.berkeley.edu points out we should testing against
  25      TeX's largest or smallest integer (32 bits), not the machine's.  So
  26      we might as well use a floating-point constant, and avoid potential
  27      compiler bugs (also noted by djb, on BSDI).  */
  28   if (r > 2147483647.0)
  29     i = 2147483647;
  30   /* should be ...8, but atof bugs are too common */
  31   else if (r < -2147483647.0)
  32     i = -2147483647;
  33   /* Admittedly some compilers don't follow the ANSI rules of casting
  34      meaning truncating toward zero; but it doesn't matter enough to do
  35      anything more complicated here.  */
  36   else if (r >= 0.0)
  37     i = (integer)(r + 0.5);
  38   else
  39     i = (integer)(r - 0.5);
  40
  41   return i;
  42 }