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Fix spurious underflows from pow with results close to 1 (bug 14811).

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This commit is contained in:
Joseph Myers 2012-11-07 13:03:31 +00:00
parent 0ab234b7db
commit 60e235ee2a
7 changed files with 96 additions and 5 deletions
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16
ChangeLog
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@ -1,3 +1,19 @@
2012-11-07 Joseph Myers <joseph@codesourcery.com>
[BZ #14811]
* sysdeps/i386/fpu/e_powl.S (pm79): New object.
(__ieee754_powl): Saturate nonzero exponents with absolute value
below 0x1p-79 to +/- 0x1p-79.
* sysdeps/ieee754/dbl-64/e_pow.c (__ieee754_pow): Saturate nonzero
exponents with absolute value below 0x1p-64 to +/- 0x1p-64.
* sysdeps/ieee754/flt-32/e_powf.c (__ieee754_powf): Saturate
nonzero exponents with absolute value below 0x1p-32 to +/-
0x1p-32.
* sysdeps/x86_64/fpu/e_powl.S (pm79): New object.
(__ieee754_powl): Saturate nonzero exponents with absolute value
below 0x1p-79 to +/- 0x1p-79.
* math/libm-test.inc (pow_test): Add more tests.
2012-11-07 Andreas Krebbel <Andreas.Krebbel@de.ibm.com> 2012-11-07 Andreas Krebbel <Andreas.Krebbel@de.ibm.com>
* sysdeps/s390/dl-procinfo.c (_dl_s390_cap_flags): Sync * sysdeps/s390/dl-procinfo.c (_dl_s390_cap_flags): Sync

2
NEWS
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@ -18,7 +18,7 @@ Version 2.17
14518, 14519, 14530, 14532, 14538, 14543, 14544, 14545, 14557, 14562, 14518, 14519, 14530, 14532, 14538, 14543, 14544, 14545, 14557, 14562,
14568, 14576, 14579, 14583, 14587, 14595, 14602, 14610, 14621, 14638, 14568, 14576, 14579, 14583, 14587, 14595, 14602, 14610, 14621, 14638,
14645, 14648, 14652, 14660, 14661, 14669, 14683, 14694, 14716, 14743, 14645, 14648, 14652, 14660, 14661, 14669, 14683, 14694, 14716, 14743,
14767, 14783, 14784, 14785, 14793, 14796, 14797, 14801, 14805. 14767, 14783, 14784, 14785, 14793, 14796, 14797, 14801, 14805, 14811.
* Support for STT_GNU_IFUNC symbols added for s390 and s390x. * Support for STT_GNU_IFUNC symbols added for s390 and s390x.
Optimized versions of memcpy, memset, and memcmp added for System z10 and Optimized versions of memcpy, memset, and memcmp added for System z10 and

29
math/libm-test.inc
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@ -7743,10 +7743,12 @@ pow_test (void)
TEST_ff_f (pow, plus_infty, 1e-7L, plus_infty); TEST_ff_f (pow, plus_infty, 1e-7L, plus_infty);
TEST_ff_f (pow, plus_infty, 1, plus_infty); TEST_ff_f (pow, plus_infty, 1, plus_infty);
TEST_ff_f (pow, plus_infty, 1e7L, plus_infty); TEST_ff_f (pow, plus_infty, 1e7L, plus_infty);
TEST_ff_f (pow, plus_infty, min_subnorm_value, plus_infty);
TEST_ff_f (pow, plus_infty, -1e-7L, 0); TEST_ff_f (pow, plus_infty, -1e-7L, 0);
TEST_ff_f (pow, plus_infty, -1, 0); TEST_ff_f (pow, plus_infty, -1, 0);
TEST_ff_f (pow, plus_infty, -1e7L, 0); TEST_ff_f (pow, plus_infty, -1e7L, 0);
TEST_ff_f (pow, plus_infty, -min_subnorm_value, 0);
TEST_ff_f (pow, minus_infty, 1, minus_infty); TEST_ff_f (pow, minus_infty, 1, minus_infty);
TEST_ff_f (pow, minus_infty, 11, minus_infty); TEST_ff_f (pow, minus_infty, 11, minus_infty);
@ -7759,6 +7761,7 @@ pow_test (void)
TEST_ff_f (pow, minus_infty, 1.1L, plus_infty); TEST_ff_f (pow, minus_infty, 1.1L, plus_infty);
TEST_ff_f (pow, minus_infty, 11.1L, plus_infty); TEST_ff_f (pow, minus_infty, 11.1L, plus_infty);
TEST_ff_f (pow, minus_infty, 1001.1L, plus_infty); TEST_ff_f (pow, minus_infty, 1001.1L, plus_infty);
TEST_ff_f (pow, minus_infty, min_subnorm_value, plus_infty);
TEST_ff_f (pow, minus_infty, -1, minus_zero); TEST_ff_f (pow, minus_infty, -1, minus_zero);
TEST_ff_f (pow, minus_infty, -11, minus_zero); TEST_ff_f (pow, minus_infty, -11, minus_zero);
@ -7771,6 +7774,7 @@ pow_test (void)
TEST_ff_f (pow, minus_infty, -1.1L, 0); TEST_ff_f (pow, minus_infty, -1.1L, 0);
TEST_ff_f (pow, minus_infty, -11.1L, 0); TEST_ff_f (pow, minus_infty, -11.1L, 0);
TEST_ff_f (pow, minus_infty, -1001.1L, 0); TEST_ff_f (pow, minus_infty, -1001.1L, 0);
TEST_ff_f (pow, minus_infty, -min_subnorm_value, 0);
#endif #endif
TEST_ff_f (pow, nan_value, nan_value, nan_value); TEST_ff_f (pow, nan_value, nan_value, nan_value);
@ -7793,6 +7797,8 @@ pow_test (void)
TEST_ff_f (pow, nan_value, minus_infty, nan_value); TEST_ff_f (pow, nan_value, minus_infty, nan_value);
TEST_ff_f (pow, nan_value, 2.5, nan_value); TEST_ff_f (pow, nan_value, 2.5, nan_value);
TEST_ff_f (pow, nan_value, -2.5, nan_value); TEST_ff_f (pow, nan_value, -2.5, nan_value);
TEST_ff_f (pow, nan_value, min_subnorm_value, nan_value);
TEST_ff_f (pow, nan_value, -min_subnorm_value, nan_value);
TEST_ff_f (pow, 1, plus_infty, 1); TEST_ff_f (pow, 1, plus_infty, 1);
TEST_ff_f (pow, -1, plus_infty, 1); TEST_ff_f (pow, -1, plus_infty, 1);
@ -7806,6 +7812,8 @@ pow_test (void)
TEST_ff_f (pow, 1, 0x1p63L, 1); TEST_ff_f (pow, 1, 0x1p63L, 1);
TEST_ff_f (pow, 1, 0x1p64L, 1); TEST_ff_f (pow, 1, 0x1p64L, 1);
TEST_ff_f (pow, 1, 0x1p72L, 1); TEST_ff_f (pow, 1, 0x1p72L, 1);
TEST_ff_f (pow, 1, min_subnorm_value, 1);
TEST_ff_f (pow, 1, -min_subnorm_value, 1);
/* pow (x, +-0) == 1. */ /* pow (x, +-0) == 1. */
TEST_ff_f (pow, plus_infty, 0, 1); TEST_ff_f (pow, plus_infty, 0, 1);
@ -7825,6 +7833,10 @@ pow_test (void)
TEST_ff_f (pow, -0.1L, -1.1L, nan_value, INVALID_EXCEPTION); TEST_ff_f (pow, -0.1L, -1.1L, nan_value, INVALID_EXCEPTION);
TEST_ff_f (pow, -10.1L, 1.1L, nan_value, INVALID_EXCEPTION); TEST_ff_f (pow, -10.1L, 1.1L, nan_value, INVALID_EXCEPTION);
TEST_ff_f (pow, -10.1L, -1.1L, nan_value, INVALID_EXCEPTION); TEST_ff_f (pow, -10.1L, -1.1L, nan_value, INVALID_EXCEPTION);
TEST_ff_f (pow, -1.01L, min_subnorm_value, nan_value, INVALID_EXCEPTION);
TEST_ff_f (pow, -1.01L, -min_subnorm_value, nan_value, INVALID_EXCEPTION);
TEST_ff_f (pow, -1.0L, min_subnorm_value, nan_value, INVALID_EXCEPTION);
TEST_ff_f (pow, -1.0L, -min_subnorm_value, nan_value, INVALID_EXCEPTION);
errno = 0; errno = 0;
TEST_ff_f (pow, 0, -1, plus_infty, DIVIDE_BY_ZERO_EXCEPTION); TEST_ff_f (pow, 0, -1, plus_infty, DIVIDE_BY_ZERO_EXCEPTION);
@ -7910,6 +7922,9 @@ pow_test (void)
TEST_ff_f (pow, 0, -11.1L, plus_infty, DIVIDE_BY_ZERO_EXCEPTION); TEST_ff_f (pow, 0, -11.1L, plus_infty, DIVIDE_BY_ZERO_EXCEPTION);
check_int ("errno for pow(0,-num) == ERANGE", errno, ERANGE, 0, 0, 0); check_int ("errno for pow(0,-num) == ERANGE", errno, ERANGE, 0, 0, 0);
errno = 0; errno = 0;
TEST_ff_f (pow, 0, -min_subnorm_value, plus_infty, DIVIDE_BY_ZERO_EXCEPTION);
check_int ("errno for pow(0,-num) == ERANGE", errno, ERANGE, 0, 0, 0);
errno = 0;
TEST_ff_f (pow, 0, -0x1p24, plus_infty, DIVIDE_BY_ZERO_EXCEPTION); TEST_ff_f (pow, 0, -0x1p24, plus_infty, DIVIDE_BY_ZERO_EXCEPTION);
check_int ("errno for pow(0,-num) == ERANGE", errno, ERANGE, 0, 0, 0); check_int ("errno for pow(0,-num) == ERANGE", errno, ERANGE, 0, 0, 0);
errno = 0; errno = 0;
@ -7925,6 +7940,9 @@ pow_test (void)
TEST_ff_f (pow, minus_zero, -11.1L, plus_infty, DIVIDE_BY_ZERO_EXCEPTION); TEST_ff_f (pow, minus_zero, -11.1L, plus_infty, DIVIDE_BY_ZERO_EXCEPTION);
check_int ("errno for pow(-0,-num) == ERANGE", errno, ERANGE, 0, 0, 0); check_int ("errno for pow(-0,-num) == ERANGE", errno, ERANGE, 0, 0, 0);
errno = 0; errno = 0;
TEST_ff_f (pow, minus_zero, -min_subnorm_value, plus_infty, DIVIDE_BY_ZERO_EXCEPTION);
check_int ("errno for pow(-0,-num) == ERANGE", errno, ERANGE, 0, 0, 0);
errno = 0;
TEST_ff_f (pow, minus_zero, -0x1p24, plus_infty, DIVIDE_BY_ZERO_EXCEPTION); TEST_ff_f (pow, minus_zero, -0x1p24, plus_infty, DIVIDE_BY_ZERO_EXCEPTION);
check_int ("errno for pow(-0,-num) == ERANGE", errno, ERANGE, 0, 0, 0); check_int ("errno for pow(-0,-num) == ERANGE", errno, ERANGE, 0, 0, 0);
errno = 0; errno = 0;
@ -8114,12 +8132,14 @@ pow_test (void)
TEST_ff_f (pow, 0.0, 0x1p24, 0.0); TEST_ff_f (pow, 0.0, 0x1p24, 0.0);
TEST_ff_f (pow, 0.0, 0x1p127, 0.0); TEST_ff_f (pow, 0.0, 0x1p127, 0.0);
TEST_ff_f (pow, 0.0, max_value, 0.0); TEST_ff_f (pow, 0.0, max_value, 0.0);
TEST_ff_f (pow, 0.0, min_subnorm_value, 0.0);
/* pow (-0, y) == +0 for y > 0 and not an odd integer. */ /* pow (-0, y) == +0 for y > 0 and not an odd integer. */
TEST_ff_f (pow, minus_zero, 4, 0.0); TEST_ff_f (pow, minus_zero, 4, 0.0);
TEST_ff_f (pow, minus_zero, 0x1p24, 0.0); TEST_ff_f (pow, minus_zero, 0x1p24, 0.0);
TEST_ff_f (pow, minus_zero, 0x1p127, 0.0); TEST_ff_f (pow, minus_zero, 0x1p127, 0.0);
TEST_ff_f (pow, minus_zero, max_value, 0.0); TEST_ff_f (pow, minus_zero, max_value, 0.0);
TEST_ff_f (pow, minus_zero, min_subnorm_value, 0.0);
TEST_ff_f (pow, 16, 0.25L, 2); TEST_ff_f (pow, 16, 0.25L, 2);
TEST_ff_f (pow, 0x1p64L, 0.125L, 256); TEST_ff_f (pow, 0x1p64L, 0.125L, 256);
@ -8407,6 +8427,15 @@ pow_test (void)
TEST_ff_f (pow, 0x1.0000000000001p0L, -0x1.23456789abcdfp61L, 1.0118762747828234466621210689458255908670e-253L); TEST_ff_f (pow, 0x1.0000000000001p0L, -0x1.23456789abcdfp61L, 1.0118762747828234466621210689458255908670e-253L);
#endif #endif
TEST_ff_f (pow, min_subnorm_value, min_subnorm_value, 1.0L);
TEST_ff_f (pow, min_subnorm_value, -min_subnorm_value, 1.0L);
TEST_ff_f (pow, max_value, min_subnorm_value, 1.0L);
TEST_ff_f (pow, max_value, -min_subnorm_value, 1.0L);
TEST_ff_f (pow, 0.99L, min_subnorm_value, 1.0L);
TEST_ff_f (pow, 0.99L, -min_subnorm_value, 1.0L);
TEST_ff_f (pow, 1.01L, min_subnorm_value, 1.0L);
TEST_ff_f (pow, 1.01L, -min_subnorm_value, 1.0L);
TEST_ff_f (pow, 2.0L, -100000.0L, plus_zero, UNDERFLOW_EXCEPTION); TEST_ff_f (pow, 2.0L, -100000.0L, plus_zero, UNDERFLOW_EXCEPTION);
END (pow); END (pow);

23
sysdeps/i386/fpu/e_powl.S
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@ -38,6 +38,9 @@ p64: .byte 0, 0, 0, 0, 0, 0, 0xf0, 0x43
.type p78,@object .type p78,@object
p78: .byte 0, 0, 0, 0, 0, 0, 0xd0, 0x44 p78: .byte 0, 0, 0, 0, 0, 0, 0xd0, 0x44
ASM_SIZE_DIRECTIVE(p78) ASM_SIZE_DIRECTIVE(p78)
.type pm79,@object
pm79: .byte 0, 0, 0, 0, 0, 0, 0, 0x3b
ASM_SIZE_DIRECTIVE(pm79)
.section .rodata.cst16,"aM",@progbits,16 .section .rodata.cst16,"aM",@progbits,16
@ -120,9 +123,25 @@ ENTRY(__ieee754_powl)
fucomp %st(1) // y : x fucomp %st(1) // y : x
fnstsw fnstsw
sahf sahf
jne 3f je 9f
/* OK, we have an integer value for y. */ // If y has absolute value at most 0x1p-79, then any finite
// nonzero x will result in 1. Saturate y to those bounds to
// avoid underflow in the calculation of y*log2(x).
fld %st // y : y : x
fabs // |y| : y : x
fcompl MO(pm79) // y : x
fnstsw
sahf
jnc 3f
fstp %st(0) // pop y
fldl MO(pm79) // 0x1p-79 : x
testb $2, %dl
jnz 3f // y > 0
fchs // -0x1p-79 : x
jmp 3f
9: /* OK, we have an integer value for y. */
popl %eax popl %eax
cfi_adjust_cfa_offset (-4) cfi_adjust_cfa_offset (-4)
popl %edx popl %edx

4
sysdeps/ieee754/dbl-64/e_pow.c
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@ -90,6 +90,10 @@ __ieee754_pow(double x, double y) {
SET_RESTORE_ROUND (FE_TONEAREST); SET_RESTORE_ROUND (FE_TONEAREST);
/* Avoid internal underflow for tiny y. The exact value of y does
not matter if |y| <= 2**-64. */
if (ABS (y) < 0x1p-64)
y = y < 0 ? -0x1p-64 : 0x1p-64;
z = log1(x,&aa,&error); /* x^y =e^(y log (X)) */ z = log1(x,&aa,&error); /* x^y =e^(y log (X)) */
t = y*134217729.0; t = y*134217729.0;
y1 = t - (t-y); y1 = t - (t-y);

4
sysdeps/ieee754/flt-32/e_powf.c
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@ -141,6 +141,10 @@ __ieee754_powf(float x, float y)
t2 = v-(t1-u); t2 = v-(t1-u);
} else { } else {
float s2,s_h,s_l,t_h,t_l; float s2,s_h,s_l,t_h,t_l;
/* Avoid internal underflow for tiny y. The exact value
of y does not matter if |y| <= 2**-32. */
if (iy < 0x2f800000)
SET_FLOAT_WORD (y, (hy & 0x80000000) | 0x2f800000);
n = 0; n = 0;
/* take care subnormal number */ /* take care subnormal number */
if(ix<0x00800000) if(ix<0x00800000)

23
sysdeps/x86_64/fpu/e_powl.S
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@ -38,6 +38,9 @@ p64: .byte 0, 0, 0, 0, 0, 0, 0xf0, 0x43
.type p78,@object .type p78,@object
p78: .byte 0, 0, 0, 0, 0, 0, 0xd0, 0x44 p78: .byte 0, 0, 0, 0, 0, 0, 0xd0, 0x44
ASM_SIZE_DIRECTIVE(p78) ASM_SIZE_DIRECTIVE(p78)
.type pm79,@object
pm79: .byte 0, 0, 0, 0, 0, 0, 0, 0x3b
ASM_SIZE_DIRECTIVE(pm79)
.section .rodata.cst16,"aM",@progbits,16 .section .rodata.cst16,"aM",@progbits,16
@ -110,9 +113,25 @@ ENTRY(__ieee754_powl)
fistpll -8(%rsp) // y : x fistpll -8(%rsp) // y : x
fildll -8(%rsp) // int(y) : y : x fildll -8(%rsp) // int(y) : y : x
fucomip %st(1),%st // y : x fucomip %st(1),%st // y : x
jne 3f je 9f
/* OK, we have an integer value for y. */ // If y has absolute value at most 0x1p-79, then any finite
// nonzero x will result in 1. Saturate y to those bounds to
// avoid underflow in the calculation of y*log2(x).
fldl MO(pm79) // 0x1p-79 : y : x
fld %st(1) // y : 0x1p-79 : y : x
fabs // |y| : 0x1p-79 : y : x
fcomip %st(1), %st // 0x1p-79 : y : x
fstp %st(0) // y : x
jnc 3f
fstp %st(0) // pop y
fldl MO(pm79) // 0x1p-79 : x
testb $2, %dl
jnz 3f // y > 0
fchs // -0x1p-79 : x
jmp 3f
9: /* OK, we have an integer value for y. */
mov -8(%rsp),%eax mov -8(%rsp),%eax
mov -4(%rsp),%edx mov -4(%rsp),%edx
orl $0, %edx orl $0, %edx