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(__floatdisf): Protect against double-rounding error.

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From-SVN: r7431
This commit is contained in:
Richard Kenner 1994-06-02 18:10:30 -04:00
parent a473029f5c
commit d9e1ab8d4e
1 changed files with 35 additions and 0 deletions
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35
gcc/libgcc2.c
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@ -1021,6 +1021,25 @@ __floatdidf (u)
#define WORD_SIZE (sizeof (SItype) * BITS_PER_UNIT)
#define HIGH_HALFWORD_COEFF (((UDItype) 1) << (WORD_SIZE / 2))
#define HIGH_WORD_COEFF (((UDItype) 1) << WORD_SIZE)
#define DI_SIZE (sizeof (DItype) * BITS_PER_UNIT)
#if TARGET_FLOAT_FORMAT == IEEE_FLOAT_FORMAT
#define DF_SIZE 53
#define SF_SIZE 24
#else
#if TARGET_FLOAT_FORMAT == IBM_FLOAT_FORMAT
#define DF_SIZE 56
#define SF_SIZE 24
#else
#if TARGET_FLOAT_FORMAT == VAX_FLOAT_FORMAT
#define DF_SIZE 56
#define SF_SIZE 24
#else
#define DF_SIZE 0
#define SF_SIZE 0
#endif
#endif
#endif
SFtype
__floatdisf (u)
@ -1035,6 +1054,22 @@ __floatdisf (u)
if (u < 0)
u = -u, negate = 1;
/* Protect against double-rounding error.
Represent any low-order bits, that might be truncated in DFmode,
by a bit that won't be lost. The bit can go in anywhere below the
rounding position of the SFmode. A fixed mask and bit position
handles all usual configurations. It doesn't handle the case
of 128-bit DImode, however. */
if (DF_SIZE < DI_SIZE
&& DF_SIZE > (DI_SIZE - DF_SIZE + SF_SIZE))
{
#define REP_BIT ((USItype) 1 << (DI_SIZE - DF_SIZE))
if (u >= ((UDItype) 1 << DF_SIZE))
{
if ((USItype) u & (REP_BIT - 1))
u |= REP_BIT;
}
}
f = (USItype) (u >> WORD_SIZE);
f *= HIGH_HALFWORD_COEFF;
f *= HIGH_HALFWORD_COEFF;