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From 91f99d323b39dc0c06c40038791db9861d4b76b9 Mon Sep 17 00:00:00 2001
From: Kito Cheng <kito.cheng@sifive.com>
Date: Mon, 12 Jul 2021 17:17:21 +0800
Subject: [PATCH] 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>
---
newlib/libc/include/math.h | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- a/newlib/libc/include/math.h
+++ b/newlib/libc/include/math.h
@@ -146,7 +146,17 @@
#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
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