求教，atan2函数有什么简易的替代品？ 第1页

       const unsigned short sintab[] = {     0x0000, 0x1918, 0x31f1, 0x4a50, 0x61f7, 0x78ad, 0x8e39, 0xa267, 0xb504, 0xc5e3,      0xd4da, 0xe1c5, 0xec82, 0xf4f9, 0xfb14, 0xfec3, 0xffff };     

       int int_asin(int x) {     int ret, sign=1;     if(x<0) {         x=-x;         sign=-1;        // 处理负数     }     for(int i = 0; i < sizeof(sintab) / sizeof(sintab[0]); i++) {         if(sintab[i] <= x && x <= sintab[i + 1]) {             ret =  (((x - sintab[i]) * 90 / (sintab[i+1] - sintab[i]) + i * 90) ) >> 4;             break;         }     }     return ret * sign; }     

       int main(void) {     for(int i = -90; i <= 90; i++) {         int y = (sin(i * 3.141593 / 180.0) * 65535.0);         int x1 = int_asin(y);          float x2 = asin(y / 65536.0) * 180.0 / 3.141593;         printf("%d %d %.3f %d
", i, x1, round(x2), x1-round(x2));     }      return 0; }