[src/trunk]: src/lib/libc/quad Corrected an off-by-one error (lib/6314 Torbjo...

[kristerw <kristerw%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/e275d9fbdd16
branches:  trunk
changeset: 467635:e275d9fbdd16
user:      kristerw <kristerw%NetBSD.org@localhost>
date:      Fri Mar 26 21:04:24 1999 +0000

description:
Corrected an off-by-one error (lib/6314 Torbjorn Granlund)

diffstat:

 lib/libc/quad/fixunsdfdi.c |  38 +++++++++++---------------------------
 1 files changed, 11 insertions(+), 27 deletions(-)

diffs (67 lines):

diff -r c32689835114 -r e275d9fbdd16 lib/libc/quad/fixunsdfdi.c
--- a/lib/libc/quad/fixunsdfdi.c        Fri Mar 26 20:53:12 1999 +0000
+++ b/lib/libc/quad/fixunsdfdi.c        Fri Mar 26 21:04:24 1999 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: fixunsdfdi.c,v 1.4 1997/07/13 20:01:45 christos Exp $  */
+/*     $NetBSD: fixunsdfdi.c,v 1.5 1999/03/26 21:04:24 kristerw Exp $  */
 
 /*-
  * Copyright (c) 1992, 1993
@@ -42,7 +42,7 @@
 #if 0
 static char sccsid[] = "@(#)fixunsdfdi.c       8.1 (Berkeley) 6/4/93";
 #else
-__RCSID("$NetBSD: fixunsdfdi.c,v 1.4 1997/07/13 20:01:45 christos Exp $");
+__RCSID("$NetBSD: fixunsdfdi.c,v 1.5 1999/03/26 21:04:24 kristerw Exp $");
 #endif
 #endif /* LIBC_SCCS and not lint */
 
@@ -61,8 +61,8 @@
 __fixunsdfdi(x)
        double x;
 {
-       double toppart;
        union uu t;
+       unsigned long tmp;
 
        if (x < 0)
                return (UQUAD_MAX);     /* ??? should be 0?  ERANGE??? */
@@ -74,30 +74,14 @@
                return (UQUAD_MAX);
 #endif
        /*
-        * Get the upper part of the result.  Note that the divide
-        * may round up; we want to avoid this if possible, so we
-        * subtract `1/2' first.
-        */
-       toppart = (x - ONE_HALF) / ONE;
-       /*
-        * Now build a u_quad_t out of the top part.  The difference
-        * between x and this is the bottom part (this may introduce
-        * a few fuzzy bits, but what the heck).  With any luck this
-        * difference will be nonnegative: x should wind up in the
-        * range [0..ULONG_MAX].  For paranoia, we assume [LONG_MIN..
-        * 2*ULONG_MAX] instead.
+        * Now we know that 0 <= x <= 18446744073709549568.  The upper
+        * limit is one ulp less than 18446744073709551615 tested for above.
+        * Dividing this by 2^32 will *not* round irrespective of any
+        * rounding modes (except if the result is an IEEE denorm).
+        * Furthermore, the quotient will fit into a 32-bit integer.
         */
-       t.ul[H] = (unsigned long)toppart;
-       t.ul[L] = 0;
-       x -= (double)t.uq;
-       if (x < 0) {
-               t.ul[H]--;
-               x += ULONG_MAX;
-       }
-       if (x > ULONG_MAX) {
-               t.ul[H]++;
-               x -= ULONG_MAX;
-       }
-       t.ul[L] = (u_long)x;
+       tmp = x / ONE;
+       t.ul[L] = (unsigned long) (x - tmp * ONE);
+       t.ul[H] = tmp;
        return (t.uq);
 }