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Introduce support for trapping math

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The feenableexcept() and fedisableexcept() APIs are now provided which
let you detect when NaNs appear the moment it happens from anywhere in
your program. Tests have also been added for the mission critical math
functions expf() and erff(), whose perfect operation has been assured.
See examples/trapping.c to see how to use this powerful functionality.
This commit is contained in:
Justine Tunney 2024-04-30 13:32:23 -07:00
parent 403bc25412
commit 5c6877b02b
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GPG key ID: BE714B4575D6E328
13 changed files with 576 additions and 2 deletions
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13
libc/runtime/cosmo.S
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@ -75,6 +75,19 @@ cosmo: push %rbp
#ifdef __FAST_MATH__
push %rax
stmxcsr (%rsp)
//
// Enable hardware optimizations in violation of the IEEE standard.
//
// - 0x0040 enables "DAZ: Denormals Are Zeros" in MXCSR. This causes the
// processor to turn denormal inputs into zero, before computing them.
// See Intel Manual Vol. 1 §10.2.3.4
//
// - 0x8000 enables "FTZ: Flush To Zero" in MXCSR. This means a floating
// point operation that results in underflow will be set to zero, with
// the same sign, rather than producing a denormalized output. It will
// happen only if underflow trapping hasnt been enabled. See the Intel
// Manual Vol. 1 §10.2.3.3.
//
orl $0x8040,(%rsp)
ldmxcsr (%rsp)
pop %rax

2
libc/runtime/fenv.h
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@ -81,6 +81,8 @@ int fesetenv(const fenv_t *);
int fesetexceptflag(const fexcept_t *, int);
int fesetround(int);
int fetestexcept(int);
int feenableexcept(int);
int fedisableexcept(int);
int feupdateenv(const fenv_t *);
int __flt_rounds(void);
int __fesetround(int);