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[ColdFire 31/63] Fix rounding problems in fpgnulib.c
This patch fixes two bugs in fpgnulib.c's __truncdfsf2. First,
it was not rounding to nearest even; it was rounding halfway cases
towards infinity instead. Second, it was not detecting overflow
in subnormal numbers (i.e. cases where a DFmode subnormal rounds
to FLT_MIN).
Richard
gcc/
200x-xx-xx Nathan Sidwell <nathan@codesourcery.com>
* config/m68k/fpgnulib.c (__truncdfsf2): Implement round to
nearest even, fix denormal rounding overflow.
Index: gcc/config/m68k/fpgnulib.c
===================================================================
--- gcc/config/m68k/fpgnulib.c 2007-01-09 15:02:03.000000000 +0000
+++ gcc/config/m68k/fpgnulib.c 2007-01-09 15:02:11.000000000 +0000
@@ -277,6 +277,8 @@ __truncdfsf2 (double a1)
register long mant;
register union float_long fl;
register union double_long dl1;
+ int sticky;
+ int shift;
dl1.d = a1;
@@ -288,29 +290,45 @@ __truncdfsf2 (double a1)
exp = EXPD (dl1) - EXCESSD + EXCESS;
+ sticky = dl1.l.lower & ((1 << 22) - 1);
+ mant = MANTD (dl1);
/* shift double mantissa 6 bits so we can round */
- mant = MANTD (dl1) >> 6;
+ sticky |= mant & ((1 << 6) - 1);
+ mant >>= 6;
/* Check for underflow and denormals. */
if (exp <= 0)
{
if (exp < -24)
- mant = 0;
+ {
+ sticky |= mant;
+ mant = 0;
+ }
else
- mant >>= 1 - exp;
+ {
+ sticky |= mant & ((1 << (1 - exp)) - 1);
+ mant >>= 1 - exp;
+ }
exp = 0;
}
- /* now round and shift down */
- mant += 1;
- mant >>= 1;
-
- /* did the round overflow? */
- if (mant & 0xFF000000L)
+ /* now round */
+ shift = 1;
+ if ((mant & 1) && (sticky || (mant & 2)))
{
- mant >>= 1;
- exp++;
+ int rounding = exp ? 2 : 1;
+
+ mant += 1;
+
+ /* did the round overflow? */
+ if (mant >= (HIDDEN << rounding))
+ {
+ exp++;
+ shift = rounding;
+ }
}
+ /* shift down */
+ mant >>= shift;
mant &= ~HIDDEN;