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| author | Szabolcs Nagy <nsz@port70.net> | 2012-12-16 17:30:29 +0100 |
|---|---|---|
| committer | Szabolcs Nagy <nsz@port70.net> | 2012-12-16 17:30:29 +0100 |
| commit | 58bba42d1bd14e1ab01f3249ffc98afdbf841a6a (patch) | |
| tree | 8790505fc53cfcd7a3bd6ecd4b1f7877018e2e17 /src/math/x86_64 | |
| parent | 525ad96e0ef6e46b6ac28438ef2ffa1d5317fb64 (diff) | |
| download | musl-58bba42d1bd14e1ab01f3249ffc98afdbf841a6a.tar.gz musl-58bba42d1bd14e1ab01f3249ffc98afdbf841a6a.tar.xz musl-58bba42d1bd14e1ab01f3249ffc98afdbf841a6a.zip | |
math: x86_64 version of expl, fixed some comments in the i386 version
Diffstat (limited to 'src/math/x86_64')
| -rw-r--r-- | src/math/x86_64/expl.s | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/src/math/x86_64/expl.s b/src/math/x86_64/expl.s index e69de29b..6d5c1ceb 100644 --- a/src/math/x86_64/expl.s +++ b/src/math/x86_64/expl.s @@ -0,0 +1,108 @@ +# exp(x) = 2^hi + 2^hi (2^lo - 1) +# where hi+lo = log2e*x with 128bit precision +# exact log2e*x calculation depends on nearest rounding mode +# using the exact multiplication method of Dekker and Veltkamp + +.global expl +.type expl,@function +expl: + fldt 8(%rsp) + + # special cases: 2*x is +-inf, nan or |x| < 0x1p-32 + # check (exponent|0x8000)+2 < 0xbfff+2-32 + movw 16(%rsp), %ax + movw %ax, %dx + orw $0x8000, %dx + addw $2, %dx + cmpw $0xbfff-30, %dx + jnb 3f + cmpw $1, %dx + jbe 1f + # if |x|<0x1p-32 return 1+x + fld1 + jmp 2f +1: testw %ax, %ax + jns 1f + # if 2*x == -inf,-nan return -0/x + fldz + fchs + fdivp + ret + # if 2*x == inf,nan return 2*x +1: fld %st(0) +2: faddp + ret + + # should be 0x1.71547652b82fe178p0 == 0x3fff b8aa3b29 5c17f0bc + # it will be wrong on non-nearest rounding mode +3: fldl2e + subq $48, %rsp + # hi = log2e_hi*x + # 2^hi = exp2l(hi) + fmul %st(1),%st + fld %st(0) + fstpt (%rsp) + fstpt 16(%rsp) + fstpt 32(%rsp) + call exp2l + # if 2^hi == inf return 2^hi + fld %st(0) + fstpt (%rsp) + cmpw $0x7fff, 8(%rsp) + je 1f + fldt 32(%rsp) + fldt 16(%rsp) + # fpu stack: 2^hi x hi + # exact mult: x*log2e + fld %st(1) + # c = 0x1p32+1 + movq $0x41f0000000100000,%rax + pushq %rax + fldl (%rsp) + # xh = x - c*x + c*x + # xl = x - xh + fmulp + fld %st(2) + fsub %st(1), %st + faddp + fld %st(2) + fsub %st(1), %st + # yh = log2e_hi - c*log2e_hi + c*log2e_hi + movq $0x3ff7154765200000,%rax + pushq %rax + fldl (%rsp) + # fpu stack: 2^hi x hi xh xl yh + # lo = hi - xh*yh + xl*yh + fld %st(2) + fmul %st(1), %st + fsubp %st, %st(4) + fmul %st(1), %st + faddp %st, %st(3) + # yl = log2e_hi - yh + movq $0x3de705fc2f000000,%rax + pushq %rax + fldl (%rsp) + # fpu stack: 2^hi x lo xh xl yl + # lo += xh*yl + xl*yl + fmul %st, %st(2) + fmulp %st, %st(1) + fxch %st(2) + faddp + faddp + # log2e_lo + movq $0xbfbe,%rax + pushq %rax + movq $0x82f0025f2dc582ee,%rax + pushq %rax + fldt (%rsp) + addq $40,%rsp + # fpu stack: 2^hi x lo log2e_lo + # lo += log2e_lo*x + # return 2^hi + 2^hi (2^lo - 1) + fmulp %st, %st(2) + faddp + f2xm1 + fmul %st(1), %st + faddp +1: addq $48, %rsp + ret |