diff options
| author | Joseph Myers <joseph@codesourcery.com> | 2020-05-07 00:45:38 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-06-10 12:10:18 -0400 |
| commit | c1c5fb8f9067c830e36830c2b82c0ec146c03d7b (patch) | |
| tree | 8f411c5fccbfae3ed5d9957587e2c5b59d33333f | |
| parent | b40eec96b26028b68c3594fbf34b6d6f029df26a (diff) | |
target/i386: fix fscale handling of infinite exponents
The fscale implementation passes infinite exponents through to generic
code that rounds the exponent to a 32-bit integer before using
floatx80_scalbn. In round-to-nearest mode, and ignoring exceptions,
this works in many cases. But it fails to handle the special cases of
scaling 0 by a +Inf exponent or an infinity by a -Inf exponent, which
should produce a NaN, and because it produces an inexact result for
finite nonzero numbers being scaled, the result is sometimes incorrect
in other rounding modes. Add appropriate handling of infinite
exponents to produce a NaN or an appropriately signed exact zero or
infinity as a result.
Signed-off-by: Joseph Myers <joseph@codesourcery.com>
Message-Id: <alpine.DEB.2.21.2005070045010.18350@digraph.polyomino.org.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | target/i386/fpu_helper.c | 22 | ||||
| -rw-r--r-- | tests/tcg/i386/test-i386-fscale.c | 29 |
2 files changed, 51 insertions, 0 deletions
diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c index 10ff90370e..72d1e77eb0 100644 --- a/target/i386/fpu_helper.c +++ b/target/i386/fpu_helper.c @@ -977,6 +977,28 @@ void helper_fscale(CPUX86State *env) float_raise(float_flag_invalid, &env->fp_status); ST0 = floatx80_silence_nan(ST0, &env->fp_status); } + } else if (floatx80_is_infinity(ST1) && + !floatx80_invalid_encoding(ST0) && + !floatx80_is_any_nan(ST0)) { + if (floatx80_is_neg(ST1)) { + if (floatx80_is_infinity(ST0)) { + float_raise(float_flag_invalid, &env->fp_status); + ST0 = floatx80_default_nan(&env->fp_status); + } else { + ST0 = (floatx80_is_neg(ST0) ? + floatx80_chs(floatx80_zero) : + floatx80_zero); + } + } else { + if (floatx80_is_zero(ST0)) { + float_raise(float_flag_invalid, &env->fp_status); + ST0 = floatx80_default_nan(&env->fp_status); + } else { + ST0 = (floatx80_is_neg(ST0) ? + floatx80_chs(floatx80_infinity) : + floatx80_infinity); + } + } } else { int n = floatx80_to_int32_round_to_zero(ST1, &env->fp_status); ST0 = floatx80_scalbn(ST0, n, &env->fp_status); diff --git a/tests/tcg/i386/test-i386-fscale.c b/tests/tcg/i386/test-i386-fscale.c index b65a055d0a..b953e7c563 100644 --- a/tests/tcg/i386/test-i386-fscale.c +++ b/tests/tcg/i386/test-i386-fscale.c @@ -31,6 +31,7 @@ int issignaling_ld(long double x) int main(void) { + short cw; int ret = 0; __asm__ volatile ("fscale" : "=t" (ld_res) : "0" (2.5L), "u" (__builtin_nansl(""))); @@ -62,5 +63,33 @@ int main(void) printf("FAIL: fscale invalid 4\n"); ret = 1; } + __asm__ volatile ("fscale" : "=t" (ld_res) : + "0" (0.0L), "u" (__builtin_infl())); + if (!isnan_ld(ld_res) || issignaling_ld(ld_res)) { + printf("FAIL: fscale 0 up inf\n"); + ret = 1; + } + __asm__ volatile ("fscale" : "=t" (ld_res) : + "0" (__builtin_infl()), "u" (-__builtin_infl())); + if (!isnan_ld(ld_res) || issignaling_ld(ld_res)) { + printf("FAIL: fscale inf down inf\n"); + ret = 1; + } + /* Set round-downward. */ + __asm__ volatile ("fnstcw %0" : "=m" (cw)); + cw = (cw & ~0xc00) | 0x400; + __asm__ volatile ("fldcw %0" : : "m" (cw)); + __asm__ volatile ("fscale" : "=t" (ld_res) : + "0" (1.0L), "u" (__builtin_infl())); + if (ld_res != __builtin_infl()) { + printf("FAIL: fscale finite up inf\n"); + ret = 1; + } + __asm__ volatile ("fscale" : "=t" (ld_res) : + "0" (-1.0L), "u" (-__builtin_infl())); + if (ld_res != -0.0L || __builtin_copysignl(1.0L, ld_res) != -1.0L) { + printf("FAIL: fscale finite down inf\n"); + ret = 1; + } return ret; } |