From 37d18660bbb1d60b4e59bf407b4b301749e0c3b9 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Thu, 6 Jan 2011 19:37:53 +0000 Subject: [PATCH] softfloat: Implement flushing input denormals to zero 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 Acked-by: Aurelien Jarno Signed-off-by: Aurelien Jarno --- fpu/softfloat.c | 104 +++++++++++++++++++++++++++++++++++++++++++++++- fpu/softfloat.h | 22 +++++++++- 2 files changed, 123 insertions(+), 3 deletions(-) diff --git a/fpu/softfloat.c b/fpu/softfloat.c index 6f5b05d5fe..17842f43da 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -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 ); diff --git a/fpu/softfloat.h b/fpu/softfloat.h index f2104c6c89..15052cc470 100644 --- a/fpu/softfloat.h +++ b/fpu/softfloat.h @@ -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); }