[Bug target/55372] MIPS: Loading integer constants to floating-pointer registers generates suboptimal code

[stevenbaker94 at rocketmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55372

--- Comment #1 from stevenbaker94 at rocketmail dot com 2013-05-01 10:16:56 UTC ---
This version handles negative numbers as well:

static inline float _fpos(const float f)
{
        union {
                float f;
                uint32_t i;
        } x;

        x.f = f;

        uint32_t r;
        float f_out;
        asm ("lui %0, %1"
                : "=d" (r)
                : "K" (x.i >> 16));
        asm ("mtc1 %1, %0"
                : "=f" (f_out)
                : "d" (r));
        return f_out;
}

static inline float _fneg(const float f)
{
        union {
                float f;
                uint32_t i;
        } x;

        x.f = f;

        uint32_t r;
        float f_out;
        asm ("lui %0, %1"
                : "=d" (r)
                : "K" (0x8000 ^ (x.i >> 16)));
        asm ("mtc1 %1, %0"
                : "=f" (f_out)
                : "d" (r));
        return f_out;
}

static inline float f(const float f)
{
        return f >= 0 ? _fpos(f) : _fneg(-f);
}

Actually, it doesn't always discard fractional bits. It works for e.g. f(0.25)
as well, since the floating-point representation still only has 0s in the lower
16 bits.