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From: "vincent-gcc at vinc17 dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/114746] With FLT_EVAL_METHOD = 2, -fexcess-precision=fast reduces the precision of floating-point constants
Date: Wed, 17 Apr 2024 23:18:38 +0000	[thread overview]
Message-ID: <bug-114746-4-Emoyu5UPTb@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114746-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114746

--- Comment #1 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
There is the same issue with constant floating-point expressions.

Consider the following program given at
  https://github.com/llvm/llvm-project/issues/89128

#include <float.h>
#include <stdio.h>

static double const_init = 1.0 + (DBL_EPSILON/2) + (DBL_EPSILON/2);
int main() {
    double nonconst_init = 1.0;
    nonconst_init = nonconst_init + (DBL_EPSILON/2) + (DBL_EPSILON/2);
    printf("FLT_EVAL_METHOD = %d\n", FLT_EVAL_METHOD);
    printf("const: %g\n", const_init - 1.0);
    printf("nonconst: %g\n", (double)nonconst_init - 1.0);
}

With -m32 -mno-sse, one gets

FLT_EVAL_METHOD = 2
const: 0
nonconst: 2.22045e-16

instead of

FLT_EVAL_METHOD = 2
const: 2.22045e-16
nonconst: 2.22045e-16

  reply	other threads:[~2024-04-17 23:18 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-16 17:51 [Bug c/114746] New: " vincent-gcc at vinc17 dot net
2024-04-17 23:18 ` vincent-gcc at vinc17 dot net [this message]
2024-04-17 23:23 ` [Bug c/114746] With FLT_EVAL_METHOD = 2, -fexcess-precision=fast reduces the precision of floating-point constants and floating-point constant expressions vincent-gcc at vinc17 dot net
2024-04-19 16:50 ` jsm28 at gcc dot gnu.org
2024-04-22  9:23 ` vincent-gcc at vinc17 dot net
2024-04-22 12:35 ` jakub at gcc dot gnu.org
2024-04-22 21:50 ` vincent-gcc at vinc17 dot net
2024-05-01 23:37 ` vincent-gcc at vinc17 dot net

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