isa-l/mem/mem_zero_detect_base.c

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#include <stdint.h>
#include <stddef.h>

int mem_zero_detect_base(void *buf, size_t n)
{
	unsigned char *c;
	uintmax_t a = 0, *p = buf;

	// Check buffer in native machine width comparisons
	while (n >= sizeof(*p)) {
		n -= sizeof(*p);
		if (*p++ != 0)
			return -1;
	}

	// Check remaining bytes
	c = (unsigned char *)p;

	switch (n) {
	case 7:
		a |= *c++;	// fall through to case 6,5,4
	case 6:
		a |= *c++;	// fall through to case 5,4
	case 5:
		a |= *c++;	// fall through to case 4
	case 4:
		a |= *((unsigned int *)c);
		break;
	case 3:
		a |= *c++;	// fall through to case 2
	case 2:
		a |= *((unsigned short *)c);
		break;
	case 1:
		a |= *c;
		break;
	}

	return (a == 0) ? 0 : -1;
}