hunt.c

来自「国外的c数值算法书籍源程序（Numerical Recipes Source- 」· C语言 代码 · 共 49 行

void hunt(float xx[], unsigned long n, float x, unsigned long *jlo)
{
	unsigned long jm,jhi,inc;
	int ascnd;

	ascnd=(xx[n] > xx[1]);
	if (*jlo <= 0 || *jlo > n) {
		*jlo=0;
		jhi=n+1;
	} else {
		inc=1;
		if (x >= xx[*jlo] == ascnd) {
			if (*jlo == n) return;
			jhi=(*jlo)+1;
			while (x >= xx[jhi] == ascnd) {
				*jlo=jhi;
				inc += inc;
				jhi=(*jlo)+inc;
				if (jhi > n) {
					jhi=n+1;
					break;
				}
			}
		} else {
			if (*jlo == 1) {
				*jlo=0;
				return;
			}
			jhi=(*jlo)--;
			while (x < xx[*jlo] == ascnd) {
				jhi=(*jlo);
				inc <<= 1;
				if (inc >= jhi) {
					*jlo=0;
					break;
				}
				else *jlo=jhi-inc;
			}
		}
	}
	while (jhi-(*jlo) != 1) {
		jm=(jhi+(*jlo)) >> 1;
		if (x > xx[jm] == ascnd)
			*jlo=jm;
		else
			jhi=jm;
	}
}