iriver Dicple D88

如何改善double、float的執行速度

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感謝QQ群友詩諾比，發現在JZ4755使用double變數時，執行速度嚴重拖慢，司徒找了一下資料，發現新增一些編譯選項可以優化double變數的執行速度，如下程式是由詩諾比提供的測試程式

main.c

#include <stdio.h>
#include <stdlib.h>

typedef signed char s8;
typedef signed short s16;
typedef signed long s32;

typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned long u32;

#define PI                  3.14159265f
#define LGE_FREQ            8000  // 22050/8000/11025
#define SND_BUF_SIZE        512
#define RTTTL_NOTES_COUNT   53  //(1+4+48)

const s16 rtttl_notes[RTTTL_NOTES_COUNT] = {
    0,    50,   100,  150,  200,
    262,  277,  294,  311,  330,  349,  370,  392,  415,  440,  466,  494,
    523,  554,  587,  622,  659,  698,  740,  784,  831,  880,  932,  988,
    1047, 1109, 1175, 1245, 1319, 1397, 1480, 1568, 1661, 1760, 1865, 1976,
    2093, 2217, 2349, 2489, 2637, 2794, 2960, 3136, 3322, 3520, 3729, 3951
};

u16 snd_len[RTTTL_NOTES_COUNT];
s8 snd_tab[RTTTL_NOTES_COUNT][SND_BUF_SIZE];

void rtttl_init(void)
{
    int wsize, qsize, fsize, rsize;
    int i, n, max_len = 0;

    memset(snd_tab[0], 0, SND_BUF_SIZE);
    snd_len[0] = 128;
    for (i = 1; i < sizeof(rtttl_notes) / sizeof(rtttl_notes[0]); i++) {
        s8* tab = snd_tab[i];
        s16 freq = rtttl_notes[i];
        u16 m = 0;
        double d_max = 1;
        s8 v = 0;
        for (n = 0; n < SND_BUF_SIZE; n++) {
            double d;
            double r = n * freq / (double)LGE_FREQ;
            d = r - (int)r;
            if (r >= 1) {
                if (d < d_max) {
                    d_max = d;
                    m = n;
                }
            }
            tab[n] = 127 * sin(2 * PI * r);
        }
        snd_len[i] = m;
    }
}

int main(int argc, char **argv)
{
    rtttl_init();
    printf("%ld, %ld\n", snd_tab[1][0], snd_len[1]);
    return 0;
}

編譯、執行

$ gcc main.c -o main -lm
$ time ./main
    real    0m8.247s
    user    0m0.780s
    sys     0m7.430s

新增編譯選項

$ gcc -mips32 -mtune=mips32 -G0 -fomit-frame-pointer -ffunction-sections -ffast-math -msoft-float -msingle-float -O3 main.c -o main -lm
$ time ./main
    real    0m1.543s
    user    0m0.260s
    sys     0m1.280s

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