float to decimal string

/*  float to decimal string, exact conversion; tested for all possible inputs against mingw 4.0 sprintf with define _XOPEN_SOURCE 1
    [email protected]
*/


void f32_to_str(float f32, char *str){
    f_un fun;
    uint32_t uv[10], mlsft, m, x, a, b, z, c;
    int i;
    char *pp, *pe, swap;
    union {
        uint64_t u64;
        uint32_t u32[2];
    } u6432;
    union {
        uint32_t u32;
        uint16_t u16[2];
    } d, t;

    fun.f = f32;
    if(fun.x == 0xFF){
        if(fun.m == 0){
            if(fun.s)
                *str++ = '-';
            strcpy(str, "inf");
        } else {
            strcpy(str, "nan");
        }
        return;
    }
    if(fun.s)
        *str++ = '-';

    x = fun.x - 127;
    m = fun.m;
    if(fun.x){
        m = fun.m | 1 << 23;
    } else {
        x++;
    }
    mlsft = x + 160 - 23;
    for(i = 0; i < 10; i++){
        uv[i] = 0;
    }

    a = mlsft >> 5;
    b = mlsft & 0x1F;
    uv[a] = m << b;
    if(b)
        uv[a + 1] = m >> (32 - b);

    pp = str;
    b = a + 1;
    do {
        for(i = b, c = z = 0; i >= 5; i--){
            t.u32 = uv[i];
            d.u16[1] = c;
            d.u16[0] = t.u16[1];
            t.u16[1] = d.u32 / 10;
            c = d.u32 % 10;

            d.u16[1] = c;
            d.u16[0] = t.u16[0];
            t.u16[0] = d.u32 / 10;
            c = d.u32 % 10;

            uv[i] = t.u32;
/*
            u6432.u32[1] = c;
            u6432.u32[0] = uv[i];
            uv[i] = u6432.u64 / 10;
            c = u6432.u64 % 10;
*/

            if(i == b && uv[i] == 0)
                b--;
            z |= uv[i];
        }
        *str++ = c + '0';
    } while(z);

    pe = str - 1;
    while(pe > pp){
        swap = *pe;
        *pe-- = *pp;
        *pp++ = swap;
    }

    *str++ = '.';

    b = a;
    do {
        for(i = b, c = z = 0; i < 5; i++){
            u6432.u64 = (uint64_t) uv[i] * 10;
            uv[i] = u6432.u32[0] + c;
            c = u6432.u32[1];
            if(uv[i] < u6432.u32[0])
                c++;
            if(i == b && uv[i] == 0)
                b++;
            z |= uv[i];
        }
        *str++ = c + '0';
    } while(z);

    *str = 0;
}