Re: lib/49256: exp2f subtests 9 and 10 of lib/libm/t_exp/exp2_values test case failing

[Tetsuya Isaki <isaki%pastel-flower.jp@localhost>]

According to Makoto Kamada's analisys,
it's a mistake to share the expected value of exp2f(7.7)
with the expected value of exp2(7.7) in tests/lib/libm/t_exp.c.

This test runs exp2f((float)7.7) = 207.93658...
but the expected value was calculated by exp2((double)7.7) = 207.93661...
This problem is only actualized with the case of 7.7 and 8.8,
but the other cases (1.1 - 6.6) has the same problem.

Here is a sample code to help to understand.

% cat a.c
#include <stdio.h>
#include <stdint.h>
#include <math.h>

int main(int ac, char *av[])
{
    float a;
    float b;

    float f = 7.7;
    double d = 7.7;

    a = (float)exp2((double)f);
    b = (float)exp2(d);
    printf("exp2((float)7.7)  = %8.8g (0x%08x)\n", a, *(uint32_t*)&a);
    printf("exp2((double)7.7) = %8.8g (0x%08x)\n", b, *(uint32_t*)&b);

    return 0;
}
% gcc a.c -lm && ./a.out
exp2((float)7.7)  = 207.93658 (0x434fefc4)
exp2((double)7.7) = 207.93661 (0x434fefc6)
%
---
Tetsuya Isaki <isaki%pastel-flower.jp@localhost / isaki%NetBSD.org@localhost>