diff options
Diffstat (limited to 'lib/msun/i387')
-rw-r--r-- | lib/msun/i387/e_exp.S | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/lib/msun/i387/e_exp.S b/lib/msun/i387/e_exp.S index 0609df0..c9a6526 100644 --- a/lib/msun/i387/e_exp.S +++ b/lib/msun/i387/e_exp.S @@ -39,7 +39,30 @@ RCSID("$FreeBSD$") /* e^x = 2^(x * log2(e)) */ ENTRY(__ieee754_exp) + /* + * If x is +-Inf, then the subtraction would give Inf-Inf = NaN. + * Avoid this. Also avoid it if x is NaN for convenience. + */ + movl 8(%esp),%eax + andl $0x7fffffff,%eax + cmpl $0x7ff00000,%eax + jae x_Inf_or_NaN + fldl 4(%esp) + + /* + * Ensure that the rounding mode is to nearest (to give the smallest + * possible fraction) and that the precision is as high as possible. + * We may as well mask interrupts if we switch the mode. + */ + fstcw 4(%esp) + movl 4(%esp),%eax + andl $0x0300,%eax + cmpl $0x0300,%eax /* RC == 0 && PC == 3? */ + je 1f /* jump if mode is good */ + movl $0x137f,8(%esp) + fldcw 8(%esp) +1: fldl2e fmulp /* x * log2(e) */ fstl %st(1) @@ -51,4 +74,23 @@ ENTRY(__ieee754_exp) faddp /* 2^(fract(x * log2(e))) */ fscale /* e^x */ fstpl %st(1) + je 1f + fldcw 4(%esp) +1: + ret + +x_Inf_or_NaN: + /* + * Return 0 if x is -Inf. Otherwise just return x, although the + * C version would return (x + x) (Real Indefinite) if x is a NaN. + */ + cmpl $0xfff00000,8(%esp) + jne x_not_minus_Inf + cmpl $0,4(%esp) + jne x_not_minus_Inf + fldz + ret + +x_not_minus_Inf: + fldl 4(%esp) ret |