https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=91f99d323b39dc0c06c40038791db9861d4b76b9 commit 91f99d323b39dc0c06c40038791db9861d4b76b9 Author: Kito Cheng <kito.cheng@sifive.com> Date: Mon Jul 12 17:17:21 2021 +0800 Minimal support for ISO/IEC TS 18661-3. - GCC will set __FLT_EVAL_METHOD__ to 16 if __fp16 supported, e.g. cortex-a55/aarch64. - $ aarch64-unknown-elf-gcc -v 2>&1 |grep version gcc version 9.2.0 (GCC) - $ aarch64-unknown-elf-gcc -E -dM -mcpu=cortex-a55 - < /dev/null |grep FLT_EVAL_METHOD #define __FLT_EVAL_METHOD__ 16 #define __FLT_EVAL_METHOD_TS_18661_3__ 16 #define __FLT_EVAL_METHOD_C99__ 16 - The behavior of __FLT_EVAL_METHOD__ == 16 is same as __FLT_EVAL_METHOD__ == 0 except for float16_t, but newlib didn't support float16_t. ISO/IEC TS 18661-3: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2405.pdf V2 Changes: - List Howland, Craig D as co-author since he provide the draft of comment in math.h. Co-authored-by: "Howland, Craig D" <howland@LGSInnovations.com> Diff: --- newlib/libc/include/math.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/newlib/libc/include/math.h b/newlib/libc/include/math.h index ba1a8a17e..0b6494e6a 100644 --- a/newlib/libc/include/math.h +++ b/newlib/libc/include/math.h @@ -146,7 +146,17 @@ extern int isnan (double); #define __TMP_FLT_EVAL_METHOD #endif /* FLT_EVAL_METHOD */ #if defined FLT_EVAL_METHOD - #if FLT_EVAL_METHOD == 0 +/* FLT_EVAL_METHOD == 16 has meaning as defined in ISO/IEC TS 18661-3, + * which provides non-compliant extensions to C and POSIX (by adding + * additional positive values for FLT_EVAL_METHOD). It effectively has + * same meaning as the C99 and C11 definitions for value 0, while also + * serving as a flag that the _Float16 (float16_t) type exists. + * + * FLT_EVAL_METHOD could be any number of bits of supported floating point + * format (e.g. 32, 64, 128), but currently only AArch64 and few other targets + * might define that as 16. */ + #if (FLT_EVAL_METHOD == 0) \ + || (FLT_EVAL_METHOD == 16) typedef float float_t; typedef double double_t; #elif FLT_EVAL_METHOD == 1