diff options
| author | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2018-07-04 12:29:29 +0100 |
|---|---|---|
| committer | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2018-08-10 17:23:16 +0100 |
| commit | 43cfdf8f4811c63bca8a2185d82a6d92977a125b (patch) | |
| tree | 36dc4519018a6e0556946f1032213f41850c375a /sysdeps/ieee754 | |
| parent | 690652882b499defb3d950dfeff8fe421d13cab5 (diff) | |
| download | glibc-43cfdf8f4811c63bca8a2185d82a6d92977a125b.tar.gz glibc-43cfdf8f4811c63bca8a2185d82a6d92977a125b.tar.xz glibc-43cfdf8f4811c63bca8a2185d82a6d92977a125b.zip | |
Clean up converttoint handling and document the semantics
This patch currently only affects aarch64. The roundtoint and converttoint internal functions are only called with small values, so 32 bit result is enough for converttoint and it is a signed int conversion so the return type is changed to int32_t. The original idea was to help the compiler keeping the result in uint64_t, then it's clear that no sign extension is needed and there is no accidental undefined or implementation defined signed int arithmetics. But it turns out gcc does a good job with inlining so changing the type has no overhead and the semantics of the conversion is less surprising this way. Since we want to allow the asuint64 (x + 0x1.8p52) style conversion, the top bits were never usable and the existing code ensures that only the bottom 32 bits of the conversion result are used. On aarch64 the neon intrinsics (which round ties to even) are changed to round and lround (which round ties away from zero) this does not affect the results in a significant way, but more portable (relies on round and lround being inlined which works with -fno-math-errno). The TOINT_SHIFT and TOINT_RINT macros were removed, only keep separate code paths for TOINT_INTRINSICS and !TOINT_INTRINSICS. * sysdeps/aarch64/fpu/math_private.h (roundtoint): Use round. (converttoint): Use lround. * sysdeps/ieee754/flt-32/math_config.h (roundtoint): Declare and document the semantics when TOINT_INTRINSICS is set. (converttoint): Likewise. (TOINT_RINT): Remove. (TOINT_SHIFT): Remove. * sysdeps/ieee754/flt-32/e_expf.c (__expf): Remove the TOINT_RINT code path.
Diffstat (limited to 'sysdeps/ieee754')
| -rw-r--r-- | sysdeps/ieee754/flt-32/e_expf.c | 5 | ||||
| -rw-r--r-- | sysdeps/ieee754/flt-32/math_config.h | 20 |
2 files changed, 16 insertions, 9 deletions
diff --git a/sysdeps/ieee754/flt-32/e_expf.c b/sysdeps/ieee754/flt-32/e_expf.c index f2238bfd74..384a586172 100644 --- a/sysdeps/ieee754/flt-32/e_expf.c +++ b/sysdeps/ieee754/flt-32/e_expf.c @@ -85,10 +85,7 @@ __expf (float x) #if TOINT_INTRINSICS kd = roundtoint (z); ki = converttoint (z); -#elif TOINT_RINT - kd = rint (z); - ki = (long) kd; -#elif TOINT_SHIFT +#else # define SHIFT __exp2f_data.shift kd = math_narrow_eval ((double) (z + SHIFT)); /* Needs to be double. */ ki = asuint64 (kd); diff --git a/sysdeps/ieee754/flt-32/math_config.h b/sysdeps/ieee754/flt-32/math_config.h index 9c4ef30173..8ca7532686 100644 --- a/sysdeps/ieee754/flt-32/math_config.h +++ b/sysdeps/ieee754/flt-32/math_config.h @@ -38,13 +38,23 @@ #endif #ifndef TOINT_INTRINSICS +/* When set, the roundtoint and converttoint functions are provided with + the semantics documented below. */ # define TOINT_INTRINSICS 0 #endif -#ifndef TOINT_RINT -# define TOINT_RINT 0 -#endif -#ifndef TOINT_SHIFT -# define TOINT_SHIFT 1 + +#if TOINT_INTRINSICS +/* Round x to nearest int in all rounding modes, ties have to be rounded + consistently with converttoint so the results match. If the result + would be outside of [-2^31, 2^31-1] then the semantics is unspecified. */ +static inline double_t +roundtoint (double_t x); + +/* Convert x to nearest int in all rounding modes, ties have to be rounded + consistently with roundtoint. If the result is not representible in an + int32_t then the semantics is unspecified. */ +static inline int32_t +converttoint (double_t x); #endif static inline uint32_t |