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From: Neha Gowda <neha.gnu.gcc@gmail.com>
Date: Tue, 18 Sep 2018 12:22:00 -0000
Message-ID: <CAODCPrOyjmXid=Rc_xagiud+t=b=u6DYGGBQs3z=AEAs+4JH6g@mail.gmail.com>
Subject: Should rand() return a RAND_MAX value for 32 bit target?
To: gcc-help@gcc.gnu.org
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X-SW-Source: 2018-09/txt/msg00049.txt.bz2

Hi,

I am trying to run the following testcase for Random Number Generator
function.
The testcase returns true when generated number is RAND_MAX and returns
false when its not generated.

Command :- gcc -m32 -O2 test.c
======================================================
#include <stdio.h>
#include <stdlib.h>

int main()
{
    unsigned int i;
    float f;
    srand(0);
    for (i = 0; i <= RAND_MAX; i++) {
        f = rand();
        if (f == RAND_MAX) {
                printf("True\n");
            return 0;
        }
    }
        printf("False\n");
    return 1;
}
======================================================
Tried them on the latest source and observed that the RAND_MAX is generated
when
the optimization is not enabled. When optimization is enabled for 32 bit
target RAND_MAX
is not being generated. However, 64 bit generates RAND_MAX with or without
optimization.

On further investigation, I found that the expand phase is optimizing the
following and hence
the RAND_MAX value is not being generated.
=========================================
Replacing Expressions
f_10 replace with --> f_10 = (float) _1;
=========================================

Can you please let me know if its the expected behavior or some bug?

Thanks,
Neha