pow_qq.c

来自「在Linxu程序设计当中」· C语言 代码 · 共 40 行

#include "f2c.h"
#ifdef __cplusplus
extern "C" {
#endif

#ifdef KR_headers
longint pow_qq(ap, bp) longint *ap, *bp;
#else
longint pow_qq(longint *ap, longint *bp)
#endif
{
	longint pow, x, n;
	unsigned long long u;	/* system-dependent */

	x = *ap;
	n = *bp;

	if (n <= 0) {
		if (n == 0 || x == 1)
			return 1;
		if (x != -1)
			return x == 0 ? 1/x : 0;
		n = -n;
		}
	u = n;
	for(pow = 1; ; )
		{
		if(u & 01)
			pow *= x;
		if(u >>= 1)
			x *= x;
		else
			break;
		}
	return(pow);
	}
#ifdef __cplusplus
}
#endif