From 7537c2b4a363237534c96d089a02b0712b49d890 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 4 May 2020 23:37:54 +0000 Subject: [PATCH 1/4] softfloat: silence sNaN for conversions to/from floatx80 Conversions between IEEE floating-point formats should convert signaling NaNs to quiet NaNs. Most of those in QEMU's softfloat code do so, but those for floatx80 fail to. Fix those conversions to silence signaling NaNs as well. Signed-off-by: Joseph Myers Message-Id: Signed-off-by: Richard Henderson --- fpu/softfloat.c | 24 +++++++--- tests/tcg/i386/test-i386-snan-convert.c | 63 +++++++++++++++++++++++++ 2 files changed, 81 insertions(+), 6 deletions(-) create mode 100644 tests/tcg/i386/test-i386-snan-convert.c diff --git a/fpu/softfloat.c b/fpu/softfloat.c index ae6ba71854..ac116c70b8 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -4498,7 +4498,9 @@ floatx80 float32_to_floatx80(float32 a, float_status *status) aSign = extractFloat32Sign( a ); if ( aExp == 0xFF ) { if (aSig) { - return commonNaNToFloatx80(float32ToCommonNaN(a, status), status); + floatx80 res = commonNaNToFloatx80(float32ToCommonNaN(a, status), + status); + return floatx80_silence_nan(res, status); } return packFloatx80(aSign, floatx80_infinity_high, @@ -5016,7 +5018,9 @@ floatx80 float64_to_floatx80(float64 a, float_status *status) aSign = extractFloat64Sign( a ); if ( aExp == 0x7FF ) { if (aSig) { - return commonNaNToFloatx80(float64ToCommonNaN(a, status), status); + floatx80 res = commonNaNToFloatx80(float64ToCommonNaN(a, status), + status); + return floatx80_silence_nan(res, status); } return packFloatx80(aSign, floatx80_infinity_high, @@ -5618,7 +5622,9 @@ float32 floatx80_to_float32(floatx80 a, float_status *status) aSign = extractFloatx80Sign( a ); if ( aExp == 0x7FFF ) { if ( (uint64_t) ( aSig<<1 ) ) { - return commonNaNToFloat32(floatx80ToCommonNaN(a, status), status); + float32 res = commonNaNToFloat32(floatx80ToCommonNaN(a, status), + status); + return float32_silence_nan(res, status); } return packFloat32( aSign, 0xFF, 0 ); } @@ -5650,7 +5656,9 @@ float64 floatx80_to_float64(floatx80 a, float_status *status) aSign = extractFloatx80Sign( a ); if ( aExp == 0x7FFF ) { if ( (uint64_t) ( aSig<<1 ) ) { - return commonNaNToFloat64(floatx80ToCommonNaN(a, status), status); + float64 res = commonNaNToFloat64(floatx80ToCommonNaN(a, status), + status); + return float64_silence_nan(res, status); } return packFloat64( aSign, 0x7FF, 0 ); } @@ -5681,7 +5689,9 @@ float128 floatx80_to_float128(floatx80 a, float_status *status) aExp = extractFloatx80Exp( a ); aSign = extractFloatx80Sign( a ); if ( ( aExp == 0x7FFF ) && (uint64_t) ( aSig<<1 ) ) { - return commonNaNToFloat128(floatx80ToCommonNaN(a, status), status); + float128 res = commonNaNToFloat128(floatx80ToCommonNaN(a, status), + status); + return float128_silence_nan(res, status); } shift128Right( aSig<<1, 0, 16, &zSig0, &zSig1 ); return packFloat128( aSign, aExp, zSig0, zSig1 ); @@ -6959,7 +6969,9 @@ floatx80 float128_to_floatx80(float128 a, float_status *status) aSign = extractFloat128Sign( a ); if ( aExp == 0x7FFF ) { if ( aSig0 | aSig1 ) { - return commonNaNToFloatx80(float128ToCommonNaN(a, status), status); + floatx80 res = commonNaNToFloatx80(float128ToCommonNaN(a, status), + status); + return floatx80_silence_nan(res, status); } return packFloatx80(aSign, floatx80_infinity_high, floatx80_infinity_low); diff --git a/tests/tcg/i386/test-i386-snan-convert.c b/tests/tcg/i386/test-i386-snan-convert.c new file mode 100644 index 0000000000..ed6d535ce2 --- /dev/null +++ b/tests/tcg/i386/test-i386-snan-convert.c @@ -0,0 +1,63 @@ +/* Test conversions of signaling NaNs to and from long double. */ + +#include +#include + +volatile float f_res; +volatile double d_res; +volatile long double ld_res; + +volatile float f_snan = __builtin_nansf(""); +volatile double d_snan = __builtin_nans(""); +volatile long double ld_snan = __builtin_nansl(""); + +int issignaling_f(float x) +{ + union { float f; uint32_t u; } u = { .f = x }; + return (u.u & 0x7fffffff) > 0x7f800000 && (u.u & 0x400000) == 0; +} + +int issignaling_d(double x) +{ + union { double d; uint64_t u; } u = { .d = x }; + return (((u.u & UINT64_C(0x7fffffffffffffff)) > + UINT64_C(0x7ff0000000000000)) && + (u.u & UINT64_C(0x8000000000000)) == 0); +} + +int issignaling_ld(long double x) +{ + union { + long double ld; + struct { uint64_t sig; uint16_t sign_exp; } s; + } u = { .ld = x }; + return ((u.s.sign_exp & 0x7fff) == 0x7fff && + (u.s.sig >> 63) != 0 && + (u.s.sig & UINT64_C(0x4000000000000000)) == 0); +} + +int main(void) +{ + int ret = 0; + ld_res = f_snan; + if (issignaling_ld(ld_res)) { + printf("FAIL: float -> long double\n"); + ret = 1; + } + ld_res = d_snan; + if (issignaling_ld(ld_res)) { + printf("FAIL: double -> long double\n"); + ret = 1; + } + f_res = ld_snan; + if (issignaling_d(f_res)) { + printf("FAIL: long double -> float\n"); + ret = 1; + } + d_res = ld_snan; + if (issignaling_d(d_res)) { + printf("FAIL: long double -> double\n"); + ret = 1; + } + return ret; +} From 41602807766e253ccb6fb761f3ff12767f786e2c Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 4 May 2020 23:38:44 +0000 Subject: [PATCH 2/4] softfloat: fix floatx80 pseudo-denormal addition / subtraction The softfloat function addFloatx80Sigs, used for addition of values with the same sign and subtraction of values with opposite sign, fails to handle the case where the two values both have biased exponent zero and there is a carry resulting from adding the significands, which can occur if one or both values are pseudo-denormals (biased exponent zero, explicit integer bit 1). Add a check for that case, so making the results match those seen on x86 hardware for pseudo-denormals. Signed-off-by: Joseph Myers Message-Id: Signed-off-by: Richard Henderson --- fpu/softfloat.c | 6 ++++++ tests/tcg/i386/test-i386-pseudo-denormal.c | 24 ++++++++++++++++++++++ 2 files changed, 30 insertions(+) create mode 100644 tests/tcg/i386/test-i386-pseudo-denormal.c diff --git a/fpu/softfloat.c b/fpu/softfloat.c index ac116c70b8..6094d267b5 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -5866,6 +5866,12 @@ static floatx80 addFloatx80Sigs(floatx80 a, floatx80 b, flag zSign, zSig1 = 0; zSig0 = aSig + bSig; if ( aExp == 0 ) { + if ((aSig | bSig) & UINT64_C(0x8000000000000000) && zSig0 < aSig) { + /* At least one of the values is a pseudo-denormal, + * and there is a carry out of the result. */ + zExp = 1; + goto shiftRight1; + } if (zSig0 == 0) { return packFloatx80(zSign, 0, 0); } diff --git a/tests/tcg/i386/test-i386-pseudo-denormal.c b/tests/tcg/i386/test-i386-pseudo-denormal.c new file mode 100644 index 0000000000..cfa2a500b0 --- /dev/null +++ b/tests/tcg/i386/test-i386-pseudo-denormal.c @@ -0,0 +1,24 @@ +/* Test pseudo-denormal operations. */ + +#include +#include + +union u { + struct { uint64_t sig; uint16_t sign_exp; } s; + long double ld; +}; + +volatile union u ld_pseudo_m16382 = { .s = { UINT64_C(1) << 63, 0 } }; + +volatile long double ld_res; + +int main(void) +{ + int ret = 0; + ld_res = ld_pseudo_m16382.ld + ld_pseudo_m16382.ld; + if (ld_res != 0x1p-16381L) { + printf("FAIL: pseudo-denormal add\n"); + ret = 1; + } + return ret; +} From be53fa785ab766d2722628403edee75b3e6ab599 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 4 May 2020 23:39:39 +0000 Subject: [PATCH 3/4] softfloat: fix floatx80 pseudo-denormal comparisons The softfloat floatx80 comparisons fail to allow for pseudo-denormals, which should compare equal to corresponding values with biased exponent 1 rather than 0. Add an adjustment for that case when comparing numbers with the same sign. Signed-off-by: Joseph Myers Message-Id: Signed-off-by: Richard Henderson --- fpu/softfloat.c | 7 +++++++ tests/tcg/i386/test-i386-pseudo-denormal.c | 4 ++++ 2 files changed, 11 insertions(+) diff --git a/fpu/softfloat.c b/fpu/softfloat.c index 6094d267b5..c57f72e3a6 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -7966,6 +7966,13 @@ static inline int floatx80_compare_internal(floatx80 a, floatx80 b, return 1 - (2 * aSign); } } else { + /* Normalize pseudo-denormals before comparison. */ + if ((a.high & 0x7fff) == 0 && a.low & UINT64_C(0x8000000000000000)) { + ++a.high; + } + if ((b.high & 0x7fff) == 0 && b.low & UINT64_C(0x8000000000000000)) { + ++b.high; + } if (a.low == b.low && a.high == b.high) { return float_relation_equal; } else { diff --git a/tests/tcg/i386/test-i386-pseudo-denormal.c b/tests/tcg/i386/test-i386-pseudo-denormal.c index cfa2a500b0..acf2b9cf03 100644 --- a/tests/tcg/i386/test-i386-pseudo-denormal.c +++ b/tests/tcg/i386/test-i386-pseudo-denormal.c @@ -20,5 +20,9 @@ int main(void) printf("FAIL: pseudo-denormal add\n"); ret = 1; } + if (ld_pseudo_m16382.ld != 0x1p-16382L) { + printf("FAIL: pseudo-denormal compare\n"); + ret = 1; + } return ret; } From 9ecaf5ccec13ff2e8fe1e72f6e0f3367d2169c1c Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 4 May 2020 23:40:20 +0000 Subject: [PATCH 4/4] softfloat: fix floatx80 pseudo-denormal round to integer The softfloat function floatx80_round_to_int incorrectly handles the case of a pseudo-denormal where only the high bit of the significand is set, ignoring that bit (treating the number as an exact zero) rather than treating the number as an alternative representation of +/- 2^-16382 (which may round to +/- 1 depending on the rounding mode) as hardware does. Fix this check (simplifying the code in the process). Signed-off-by: Joseph Myers Message-Id: Signed-off-by: Richard Henderson --- fpu/softfloat.c | 2 +- tests/tcg/i386/test-i386-pseudo-denormal.c | 10 ++++++++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/fpu/softfloat.c b/fpu/softfloat.c index c57f72e3a6..a362bf89ca 100644 --- a/fpu/softfloat.c +++ b/fpu/softfloat.c @@ -5741,7 +5741,7 @@ floatx80 floatx80_round_to_int(floatx80 a, float_status *status) } if ( aExp < 0x3FFF ) { if ( ( aExp == 0 ) - && ( (uint64_t) ( extractFloatx80Frac( a )<<1 ) == 0 ) ) { + && ( (uint64_t) ( extractFloatx80Frac( a ) ) == 0 ) ) { return a; } status->float_exception_flags |= float_flag_inexact; diff --git a/tests/tcg/i386/test-i386-pseudo-denormal.c b/tests/tcg/i386/test-i386-pseudo-denormal.c index acf2b9cf03..00d510cf4a 100644 --- a/tests/tcg/i386/test-i386-pseudo-denormal.c +++ b/tests/tcg/i386/test-i386-pseudo-denormal.c @@ -14,6 +14,7 @@ volatile long double ld_res; int main(void) { + short cw; int ret = 0; ld_res = ld_pseudo_m16382.ld + ld_pseudo_m16382.ld; if (ld_res != 0x1p-16381L) { @@ -24,5 +25,14 @@ int main(void) printf("FAIL: pseudo-denormal compare\n"); ret = 1; } + /* Set round-upward. */ + __asm__ volatile ("fnstcw %0" : "=m" (cw)); + cw = (cw & ~0xc00) | 0x800; + __asm__ volatile ("fldcw %0" : : "m" (cw)); + __asm__ ("frndint" : "=t" (ld_res) : "0" (ld_pseudo_m16382.ld)); + if (ld_res != 1.0L) { + printf("FAIL: pseudo-denormal round-to-integer\n"); + ret = 1; + } return ret; }