From 7d09d0e26191c1ca66c25dcfe0e62328ce87276f Mon Sep 17 00:00:00 2001 From: Thomas Preudhomme Date: Tue, 23 Jan 2018 10:43:54 +0000 Subject: [PATCH] Disable powf/log2?f/exp2?f optimization for single-precision Arm FPU New optimized powf, logf, log2f, expf and exp2f yield worse performance on Arm targets with only single precision instructions because the double precision arithmetic is then implemented via softfloat routines. This patch uses the old implementation when double precision instructions are not available on Arm targets. Testing: Built newlib with GCC's rmprofile Arm multilibs and compared before/after -> only the above functions are changed and calls to them (name change from logf to __ieee754_logf and similar). Testing the changed function on a panel of values yields the same result before the original patches to improve them and after this one. Double checking the performance by looping the same panel of values being tested on Arm Cortex-M4 does show the performance regression is fixed. --- newlib/libc/include/machine/ieeefp.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/newlib/libc/include/machine/ieeefp.h b/newlib/libc/include/machine/ieeefp.h index b1b44665e..9fbef8449 100644 --- a/newlib/libc/include/machine/ieeefp.h +++ b/newlib/libc/include/machine/ieeefp.h @@ -78,7 +78,9 @@ # else # define __IEEE_BIG_ENDIAN # endif -# define __OBSOLETE_MATH_DEFAULT 0 +# if __ARM_FP & 0x8 +# define __OBSOLETE_MATH_DEFAULT 0 +# endif #else # define __IEEE_BIG_ENDIAN # ifdef __ARMEL__