diff options
| author | Joseph Myers <joseph@codesourcery.com> | 2012-11-28 13:40:54 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2012-11-28 13:40:54 +0000 |
| commit | 1bead169c32a3a688de863709b863207b7aafddd (patch) | |
| tree | 7c3dcf66e7b4d92a9bcc5e3bb67f2cbbb19172f3 /sysdeps/x86_64 | |
| parent | 0817d63dd1f8e165f8ef6590bf4feddf06705381 (diff) | |
| download | glibc-1bead169c32a3a688de863709b863207b7aafddd.tar.gz glibc-1bead169c32a3a688de863709b863207b7aafddd.tar.xz glibc-1bead169c32a3a688de863709b863207b7aafddd.zip | |
Fix powl inaccuracy for x86_64 and x86 (bug 13881).
Diffstat (limited to 'sysdeps/x86_64')
| -rw-r--r-- | sysdeps/x86_64/fpu/e_powl.S | 52 | ||||
| -rw-r--r-- | sysdeps/x86_64/fpu/libm-test-ulps | 4 |
2 files changed, 26 insertions, 30 deletions
diff --git a/sysdeps/x86_64/fpu/e_powl.S b/sysdeps/x86_64/fpu/e_powl.S index 1b3718522d..ff96cec68a 100644 --- a/sysdeps/x86_64/fpu/e_powl.S +++ b/sysdeps/x86_64/fpu/e_powl.S @@ -26,9 +26,9 @@ .type one,@object one: .double 1.0 ASM_SIZE_DIRECTIVE(one) - .type limit,@object -limit: .double 0.29 - ASM_SIZE_DIRECTIVE(limit) + .type p3,@object +p3: .byte 0, 0, 0, 0, 0, 0, 0x20, 0x40 + ASM_SIZE_DIRECTIVE(p3) .type p63,@object p63: .byte 0, 0, 0, 0, 0, 0, 0xe0, 0x43 ASM_SIZE_DIRECTIVE(p63) @@ -131,7 +131,15 @@ ENTRY(__ieee754_powl) fchs // -0x1p-79 : x jmp 3f -9: /* OK, we have an integer value for y. */ +9: /* OK, we have an integer value for y. Unless very small + (we use < 8), use the algorithm for real exponent to avoid + accumulation of errors. */ + fldl MO(p3) // 8 : y : x + fld %st(1) // y : 8 : y : x + fabs // |y| : 8 : y : x + fcomip %st(1), %st // 8 : y : x + fstp %st(0) // y : x + jnc 2f mov -8(%rsp),%eax mov -4(%rsp),%edx orl $0, %edx @@ -167,7 +175,7 @@ ENTRY(__ieee754_powl) ret .align ALIGNARG(4) -2: // y is a large integer (absolute value at least 1L<<63), but +2: // y is a large integer (absolute value at least 8), but // may be odd unless at least 1L<<64. So it may be necessary // to adjust the sign of a negative result afterwards. fxch // x : y @@ -190,31 +198,15 @@ ENTRY(__ieee754_powl) fchs // -(1L<<78) : |x| .align ALIGNARG(4) 3: /* y is a real number. */ - fxch // x : y - fldl MO(one) // 1.0 : x : y - fldl MO(limit) // 0.29 : 1.0 : x : y - fld %st(2) // x : 0.29 : 1.0 : x : y - fsub %st(2) // x-1 : 0.29 : 1.0 : x : y - fabs // |x-1| : 0.29 : 1.0 : x : y - fucompp // 1.0 : x : y - fnstsw - fxch // x : 1.0 : y - test $0x4500,%eax - jz 7f - fsub %st(1) // x-1 : 1.0 : y - fyl2xp1 // log2(x) : y - jmp 8f - -7: fyl2x // log2(x) : y -8: fmul %st(1) // y*log2(x) : y - fst %st(1) // y*log2(x) : y*log2(x) - frndint // int(y*log2(x)) : y*log2(x) - fsubr %st, %st(1) // int(y*log2(x)) : fract(y*log2(x)) - fxch // fract(y*log2(x)) : int(y*log2(x)) - f2xm1 // 2^fract(y*log2(x))-1 : int(y*log2(x)) - faddl MO(one) // 2^fract(y*log2(x)) : int(y*log2(x)) - fscale // 2^fract(y*log2(x))*2^int(y*log2(x)) : int(y*log2(x)) - fstp %st(1) // 2^fract(y*log2(x))*2^int(y*log2(x)) + subq $40, %rsp + cfi_adjust_cfa_offset (40) + fstpt 16(%rsp) // x + fstpt (%rsp) // <empty> + mov %edx, 32(%rsp) + call HIDDEN_JUMPTARGET (__powl_helper) // <result> + mov 32(%rsp), %edx + addq $40, %rsp + cfi_adjust_cfa_offset (-40) testb $2, %dh jz 292f // x is negative. If y is an odd integer, negate the result. diff --git a/sysdeps/x86_64/fpu/libm-test-ulps b/sysdeps/x86_64/fpu/libm-test-ulps index f33dfed3df..9e7a8adac3 100644 --- a/sysdeps/x86_64/fpu/libm-test-ulps +++ b/sysdeps/x86_64/fpu/libm-test-ulps @@ -2398,6 +2398,8 @@ ifloat: 1 Test "pow (0x0.ffffffp0, -0x1p24) == 2.7182819094701610539628664526874952929416": float: 1 ifloat: 1 +ildouble: 1 +ldouble: 1 Test "pow (0x0.ffffffp0, 0x1p24) == 0.3678794302077803437135155590023422899744": float: 1 ifloat: 1 @@ -3575,6 +3577,8 @@ ifloat: 1 Function: "pow": float: 1 ifloat: 1 +ildouble: 1 +ldouble: 1 Function: "pow_downward": float: 1 |