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softfloat: Implement flushing input denormals to zero

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Add support to softfloat for flushing input denormal float32 and float64
to zero. softfloat's existing 'flush_to_zero' flag only flushes denormals
to zero on output. Some CPUs need input denormals to be flushed before
processing as well. Implement this, using a new status flag to enable it
and a new exception status bit to indicate when it has happened. Existing
CPUs should be unaffected as there is no behaviour change unless the
mode is enabled.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Peter Maydell 2011-01-06 19:37:53 +00:00 committed by Aurelien Jarno
parent 838fa72d0b
commit 37d18660bb
2 changed files with 123 additions and 3 deletions
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104
fpu/softfloat.c
View File

@ -30,8 +30,6 @@ these four paragraphs for those parts of this code that are retained.
=============================================================================*/
/* FIXME: Flush-To-Zero only effects results. Denormal inputs should also
be flushed to zero. */
#include "softfloat.h"
/*----------------------------------------------------------------------------
@ -203,6 +201,21 @@ INLINE flag extractFloat32Sign( float32 a )
}
/*----------------------------------------------------------------------------
| If `a' is denormal and we are in flush-to-zero mode then set the
| input-denormal exception and return zero. Otherwise just return the value.
*----------------------------------------------------------------------------*/
static float32 float32_squash_input_denormal(float32 a STATUS_PARAM)
{
if (STATUS(flush_inputs_to_zero)) {
if (extractFloat32Exp(a) == 0 && extractFloat32Frac(a) != 0) {
float_raise(float_flag_input_denormal STATUS_VAR);
return make_float32(float32_val(a) & 0x80000000);
}
}
return a;
}
/*----------------------------------------------------------------------------
| Normalizes the subnormal single-precision floating-point value represented
| by the denormalized significand `aSig'. The normalized exponent and
@ -367,6 +380,21 @@ INLINE flag extractFloat64Sign( float64 a )
}
/*----------------------------------------------------------------------------
| If `a' is denormal and we are in flush-to-zero mode then set the
| input-denormal exception and return zero. Otherwise just return the value.
*----------------------------------------------------------------------------*/
static float64 float64_squash_input_denormal(float64 a STATUS_PARAM)
{
if (STATUS(flush_inputs_to_zero)) {
if (extractFloat64Exp(a) == 0 && extractFloat64Frac(a) != 0) {
float_raise(float_flag_input_denormal STATUS_VAR);
return make_float64(float64_val(a) & (1ULL << 63));
}
}
return a;
}
/*----------------------------------------------------------------------------
| Normalizes the subnormal double-precision floating-point value represented
| by the denormalized significand `aSig'. The normalized exponent and
@ -1298,6 +1326,7 @@ int32 float32_to_int32( float32 a STATUS_PARAM )
bits32 aSig;
bits64 aSig64;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
aSign = extractFloat32Sign( a );
@ -1327,6 +1356,7 @@ int32 float32_to_int32_round_to_zero( float32 a STATUS_PARAM )
int16 aExp, shiftCount;
bits32 aSig;
int32 z;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -1418,6 +1448,7 @@ int64 float32_to_int64( float32 a STATUS_PARAM )
int16 aExp, shiftCount;
bits32 aSig;
bits64 aSig64, aSigExtra;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -1455,6 +1486,7 @@ int64 float32_to_int64_round_to_zero( float32 a STATUS_PARAM )
bits32 aSig;
bits64 aSig64;
int64 z;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -1496,6 +1528,7 @@ float64 float32_to_float64( float32 a STATUS_PARAM )
flag aSign;
int16 aExp;
bits32 aSig;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -1528,6 +1561,7 @@ floatx80 float32_to_floatx80( float32 a STATUS_PARAM )
int16 aExp;
bits32 aSig;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
aSign = extractFloat32Sign( a );
@ -1561,6 +1595,7 @@ float128 float32_to_float128( float32 a STATUS_PARAM )
int16 aExp;
bits32 aSig;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
aSign = extractFloat32Sign( a );
@ -1593,6 +1628,7 @@ float32 float32_round_to_int( float32 a STATUS_PARAM)
bits32 lastBitMask, roundBitsMask;
int8 roundingMode;
bits32 z;
a = float32_squash_input_denormal(a STATUS_VAR);
aExp = extractFloat32Exp( a );
if ( 0x96 <= aExp ) {
@ -1796,6 +1832,8 @@ static float32 subFloat32Sigs( float32 a, float32 b, flag zSign STATUS_PARAM)
float32 float32_add( float32 a, float32 b STATUS_PARAM )
{
flag aSign, bSign;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
aSign = extractFloat32Sign( a );
bSign = extractFloat32Sign( b );
@ -1817,6 +1855,8 @@ float32 float32_add( float32 a, float32 b STATUS_PARAM )
float32 float32_sub( float32 a, float32 b STATUS_PARAM )
{
flag aSign, bSign;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
aSign = extractFloat32Sign( a );
bSign = extractFloat32Sign( b );
@ -1843,6 +1883,9 @@ float32 float32_mul( float32 a, float32 b STATUS_PARAM )
bits64 zSig64;
bits32 zSig;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
aSign = extractFloat32Sign( a );
@ -1900,6 +1943,8 @@ float32 float32_div( float32 a, float32 b STATUS_PARAM )
flag aSign, bSign, zSign;
int16 aExp, bExp, zExp;
bits32 aSig, bSig, zSig;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -1966,6 +2011,8 @@ float32 float32_rem( float32 a, float32 b STATUS_PARAM )
bits64 aSig64, bSig64, q64;
bits32 alternateASig;
sbits32 sigMean;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -2062,6 +2109,7 @@ float32 float32_sqrt( float32 a STATUS_PARAM )
int16 aExp, zExp;
bits32 aSig, zSig;
bits64 rem, term;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -2148,6 +2196,7 @@ float32 float32_exp2( float32 a STATUS_PARAM )
bits32 aSig;
float64 r, x, xn;
int i;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -2194,6 +2243,7 @@ float32 float32_log2( float32 a STATUS_PARAM )
int16 aExp;
bits32 aSig, zSig, i;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
aSign = extractFloat32Sign( a );
@ -2238,6 +2288,8 @@ float32 float32_log2( float32 a STATUS_PARAM )
int float32_eq( float32 a, float32 b STATUS_PARAM )
{
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat32Exp( a ) == 0xFF ) && extractFloat32Frac( a ) )
|| ( ( extractFloat32Exp( b ) == 0xFF ) && extractFloat32Frac( b ) )
@ -2263,6 +2315,8 @@ int float32_le( float32 a, float32 b STATUS_PARAM )
{
flag aSign, bSign;
bits32 av, bv;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat32Exp( a ) == 0xFF ) && extractFloat32Frac( a ) )
|| ( ( extractFloat32Exp( b ) == 0xFF ) && extractFloat32Frac( b ) )
@ -2289,6 +2343,8 @@ int float32_lt( float32 a, float32 b STATUS_PARAM )
{
flag aSign, bSign;
bits32 av, bv;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat32Exp( a ) == 0xFF ) && extractFloat32Frac( a ) )
|| ( ( extractFloat32Exp( b ) == 0xFF ) && extractFloat32Frac( b ) )
@ -2315,6 +2371,8 @@ int float32_lt( float32 a, float32 b STATUS_PARAM )
int float32_eq_signaling( float32 a, float32 b STATUS_PARAM )
{
bits32 av, bv;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat32Exp( a ) == 0xFF ) && extractFloat32Frac( a ) )
|| ( ( extractFloat32Exp( b ) == 0xFF ) && extractFloat32Frac( b ) )
@ -2339,6 +2397,8 @@ int float32_le_quiet( float32 a, float32 b STATUS_PARAM )
{
flag aSign, bSign;
bits32 av, bv;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat32Exp( a ) == 0xFF ) && extractFloat32Frac( a ) )
|| ( ( extractFloat32Exp( b ) == 0xFF ) && extractFloat32Frac( b ) )
@ -2368,6 +2428,8 @@ int float32_lt_quiet( float32 a, float32 b STATUS_PARAM )
{
flag aSign, bSign;
bits32 av, bv;
a = float32_squash_input_denormal(a STATUS_VAR);
b = float32_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat32Exp( a ) == 0xFF ) && extractFloat32Frac( a ) )
|| ( ( extractFloat32Exp( b ) == 0xFF ) && extractFloat32Frac( b ) )
@ -2401,6 +2463,7 @@ int32 float64_to_int32( float64 a STATUS_PARAM )
flag aSign;
int16 aExp, shiftCount;
bits64 aSig;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -2429,6 +2492,7 @@ int32 float64_to_int32_round_to_zero( float64 a STATUS_PARAM )
int16 aExp, shiftCount;
bits64 aSig, savedASig;
int32 z;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -2525,6 +2589,7 @@ int64 float64_to_int64( float64 a STATUS_PARAM )
flag aSign;
int16 aExp, shiftCount;
bits64 aSig, aSigExtra;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -2568,6 +2633,7 @@ int64 float64_to_int64_round_to_zero( float64 a STATUS_PARAM )
int16 aExp, shiftCount;
bits64 aSig;
int64 z;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -2617,6 +2683,7 @@ float32 float64_to_float32( float64 a STATUS_PARAM )
int16 aExp;
bits64 aSig;
bits32 zSig;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -2694,6 +2761,7 @@ bits16 float32_to_float16( float32 a, flag ieee STATUS_PARAM)
bits32 mask;
bits32 increment;
int8 roundingMode;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
@ -2788,6 +2856,7 @@ floatx80 float64_to_floatx80( float64 a STATUS_PARAM )
int16 aExp;
bits64 aSig;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
aSign = extractFloat64Sign( a );
@ -2822,6 +2891,7 @@ float128 float64_to_float128( float64 a STATUS_PARAM )
int16 aExp;
bits64 aSig, zSig0, zSig1;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
aSign = extractFloat64Sign( a );
@ -2855,6 +2925,7 @@ float64 float64_round_to_int( float64 a STATUS_PARAM )
bits64 lastBitMask, roundBitsMask;
int8 roundingMode;
bits64 z;
a = float64_squash_input_denormal(a STATUS_VAR);
aExp = extractFloat64Exp( a );
if ( 0x433 <= aExp ) {
@ -3071,6 +3142,8 @@ static float64 subFloat64Sigs( float64 a, float64 b, flag zSign STATUS_PARAM )
float64 float64_add( float64 a, float64 b STATUS_PARAM )
{
flag aSign, bSign;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
aSign = extractFloat64Sign( a );
bSign = extractFloat64Sign( b );
@ -3092,6 +3165,8 @@ float64 float64_add( float64 a, float64 b STATUS_PARAM )
float64 float64_sub( float64 a, float64 b STATUS_PARAM )
{
flag aSign, bSign;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
aSign = extractFloat64Sign( a );
bSign = extractFloat64Sign( b );
@ -3116,6 +3191,9 @@ float64 float64_mul( float64 a, float64 b STATUS_PARAM )
int16 aExp, bExp, zExp;
bits64 aSig, bSig, zSig0, zSig1;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
aSign = extractFloat64Sign( a );
@ -3175,6 +3253,8 @@ float64 float64_div( float64 a, float64 b STATUS_PARAM )
bits64 aSig, bSig, zSig;
bits64 rem0, rem1;
bits64 term0, term1;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -3246,6 +3326,8 @@ float64 float64_rem( float64 a, float64 b STATUS_PARAM )
bits64 q, alternateASig;
sbits64 sigMean;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
aSign = extractFloat64Sign( a );
@ -3328,6 +3410,7 @@ float64 float64_sqrt( float64 a STATUS_PARAM )
int16 aExp, zExp;
bits64 aSig, zSig, doubleZSig;
bits64 rem0, rem1, term0, term1;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -3377,6 +3460,7 @@ float64 float64_log2( float64 a STATUS_PARAM )
flag aSign, zSign;
int16 aExp;
bits64 aSig, aSig0, aSig1, zSig, i;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
@ -3422,6 +3506,8 @@ float64 float64_log2( float64 a STATUS_PARAM )
int float64_eq( float64 a, float64 b STATUS_PARAM )
{
bits64 av, bv;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat64Exp( a ) == 0x7FF ) && extractFloat64Frac( a ) )
|| ( ( extractFloat64Exp( b ) == 0x7FF ) && extractFloat64Frac( b ) )
@ -3448,6 +3534,8 @@ int float64_le( float64 a, float64 b STATUS_PARAM )
{
flag aSign, bSign;
bits64 av, bv;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat64Exp( a ) == 0x7FF ) && extractFloat64Frac( a ) )
|| ( ( extractFloat64Exp( b ) == 0x7FF ) && extractFloat64Frac( b ) )
@ -3475,6 +3563,8 @@ int float64_lt( float64 a, float64 b STATUS_PARAM )
flag aSign, bSign;
bits64 av, bv;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat64Exp( a ) == 0x7FF ) && extractFloat64Frac( a ) )
|| ( ( extractFloat64Exp( b ) == 0x7FF ) && extractFloat64Frac( b ) )
) {
@ -3500,6 +3590,8 @@ int float64_lt( float64 a, float64 b STATUS_PARAM )
int float64_eq_signaling( float64 a, float64 b STATUS_PARAM )
{
bits64 av, bv;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat64Exp( a ) == 0x7FF ) && extractFloat64Frac( a ) )
|| ( ( extractFloat64Exp( b ) == 0x7FF ) && extractFloat64Frac( b ) )
@ -3524,6 +3616,8 @@ int float64_le_quiet( float64 a, float64 b STATUS_PARAM )
{
flag aSign, bSign;
bits64 av, bv;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat64Exp( a ) == 0x7FF ) && extractFloat64Frac( a ) )
|| ( ( extractFloat64Exp( b ) == 0x7FF ) && extractFloat64Frac( b ) )
@ -3553,6 +3647,8 @@ int float64_lt_quiet( float64 a, float64 b STATUS_PARAM )
{
flag aSign, bSign;
bits64 av, bv;
a = float64_squash_input_denormal(a STATUS_VAR);
b = float64_squash_input_denormal(b STATUS_VAR);
if ( ( ( extractFloat64Exp( a ) == 0x7FF ) && extractFloat64Frac( a ) )
|| ( ( extractFloat64Exp( b ) == 0x7FF ) && extractFloat64Frac( b ) )
@ -5833,6 +5929,8 @@ INLINE int float ## s ## _compare_internal( float ## s a, float ## s b, \
{ \
flag aSign, bSign; \
bits ## s av, bv; \
a = float ## s ## _squash_input_denormal(a STATUS_VAR); \
b = float ## s ## _squash_input_denormal(b STATUS_VAR); \
\
if (( ( extractFloat ## s ## Exp( a ) == nan_exp ) && \
extractFloat ## s ## Frac( a ) ) || \
@ -5929,6 +6027,7 @@ float32 float32_scalbn( float32 a, int n STATUS_PARAM )
int16 aExp;
bits32 aSig;
a = float32_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat32Frac( a );
aExp = extractFloat32Exp( a );
aSign = extractFloat32Sign( a );
@ -5952,6 +6051,7 @@ float64 float64_scalbn( float64 a, int n STATUS_PARAM )
int16 aExp;
bits64 aSig;
a = float64_squash_input_denormal(a STATUS_VAR);
aSig = extractFloat64Frac( a );
aExp = extractFloat64Exp( a );
aSign = extractFloat64Sign( a );

22
fpu/softfloat.h
View File

@ -180,7 +180,8 @@ enum {
float_flag_divbyzero = 4,
float_flag_overflow = 8,
float_flag_underflow = 16,
float_flag_inexact = 32
float_flag_inexact = 32,
float_flag_input_denormal = 64
};
typedef struct float_status {
@ -190,7 +191,10 @@ typedef struct float_status {
#ifdef FLOATX80
signed char floatx80_rounding_precision;
#endif
/* should denormalised results go to zero and set the inexact flag? */
flag flush_to_zero;
/* should denormalised inputs go to zero and set the input_denormal flag? */
flag flush_inputs_to_zero;
flag default_nan_mode;
} float_status;
@ -200,6 +204,10 @@ INLINE void set_flush_to_zero(flag val STATUS_PARAM)
{
STATUS(flush_to_zero) = val;
}
INLINE void set_flush_inputs_to_zero(flag val STATUS_PARAM)
{
STATUS(flush_inputs_to_zero) = val;
}
INLINE void set_default_nan_mode(flag val STATUS_PARAM)
{
STATUS(default_nan_mode) = val;
@ -294,11 +302,17 @@ float32 float32_scalbn( float32, int STATUS_PARAM );
INLINE float32 float32_abs(float32 a)
{
/* Note that abs does *not* handle NaN specially, nor does
* it flush denormal inputs to zero.
*/
return make_float32(float32_val(a) & 0x7fffffff);
}
INLINE float32 float32_chs(float32 a)
{
/* Note that chs does *not* handle NaN specially, nor does
* it flush denormal inputs to zero.
*/
return make_float32(float32_val(a) ^ 0x80000000);
}
@ -374,11 +388,17 @@ float64 float64_scalbn( float64, int STATUS_PARAM );
INLINE float64 float64_abs(float64 a)
{
/* Note that abs does *not* handle NaN specially, nor does
* it flush denormal inputs to zero.
*/
return make_float64(float64_val(a) & 0x7fffffffffffffffLL);
}
INLINE float64 float64_chs(float64 a)
{
/* Note that chs does *not* handle NaN specially, nor does
* it flush denormal inputs to zero.
*/
return make_float64(float64_val(a) ^ 0x8000000000000000LL);
}