string.c

jos lab3代码

// Basic string routines.  Not hardware optimized, but not shabby.

#include <inc/string.h>

int
strlen(const char *s)
{
	int n;

	for (n = 0; *s != '\0'; s++)
		n++;
	return n;
}

int
strnlen(const char *s, size_t size)
{
	int n;

	for (n = 0; size > 0 && *s != '\0'; s++, size--)
		n++;
	return n;
}

char *
strcpy(char *dst, const char *src)
{
	char *ret;

	ret = dst;
	while ((*dst++ = *src++) != '\0')
		/* do nothing */;
	return ret;
}

char *
strncpy(char *dst, const char *src, size_t size) {
	size_t i;
	char *ret;

	ret = dst;
	for (i = 0; i < size; i++) {
		*dst++ = *src;
		// If strlen(src) < size, null-pad 'dst' out to 'size' chars
		if (*src != '\0')
			src++;
	}
	return ret;
}

size_t
strlcpy(char *dst, const char *src, size_t size)
{
	char *dst_in;

	dst_in = dst;
	if (size > 0) {
		while (--size > 0 && *src != '\0')
			*dst++ = *src++;
		*dst = '\0';
	}
	return dst - dst_in;
}

int
strcmp(const char *p, const char *q)
{
	while (*p && *p == *q)
		p++, q++;
	return (int) ((unsigned char) *p - (unsigned char) *q);
}

int
strncmp(const char *p, const char *q, size_t n)
{
	while (n > 0 && *p && *p == *q)
		n--, p++, q++;
	if (n == 0)
		return 0;
	else
		return (int) ((unsigned char) *p - (unsigned char) *q);
}

// Return a pointer to the first occurrence of 'c' in 's',
// or a null pointer if the string has no 'c'.
char *
strchr(const char *s, char c)
{
	for (; *s; s++)
		if (*s == c)
			return (char *) s;
	return 0;
}

// Return a pointer to the first occurrence of 'c' in 's',
// or a pointer to the string-ending null character if the string has no 'c'.
char *
strfind(const char *s, char c)
{
	for (; *s; s++)
		if (*s == c)
			break;
	return (char *) s;
}


void *
memset(void *v, int c, size_t n)
{
	char *p;
	int m;

	p = v;
	m = n;
	while (--m >= 0)
		*p++ = c;

	return v;
}

/* no memcpy - use memmove instead */

void *
memmove(void *dst, const void *src, size_t n)
{
	const char *s;
	char *d;
	
	s = src;
	d = dst;
	if (s < d && s + n > d) {
		s += n;
		d += n;
		while (n-- > 0)
			*--d = *--s;
	} else
		while (n-- > 0)
			*d++ = *s++;

	return dst;
}

/* sigh - gcc emits references to this for structure assignments! */
/* it is *not* prototyped in inc/string.h - do not use directly. */
void *
memcpy(void *dst, void *src, size_t n)
{
	return memmove(dst, src, n);
}

int
memcmp(const void *v1, const void *v2, size_t n)
{
	const uint8_t *s1 = (const uint8_t *) v1;
	const uint8_t *s2 = (const uint8_t *) v2;

	while (n-- > 0) {
		if (*s1 != *s2)
			return (int) *s1 - (int) *s2;
		s1++, s2++;
	}

	return 0;
}

void *
memfind(const void *s, int c, size_t n)
{
	const void *ends = (const char *) s + n;
	for (; s < ends; s++)
		if (*(const unsigned char *) s == (unsigned char) c)
			break;
	return (void *) s;
}

long
strtol(const char *s, char **endptr, int base)
{
	int neg = 0;
	long val = 0;

	// gobble initial whitespace
	while (*s == ' ' || *s == '\t')
		s++;

	// plus/minus sign
	if (*s == '+')
		s++;
	else if (*s == '-')
		s++, neg = 1;

	// hex or octal base prefix
	if ((base == 0 || base == 16) && (s[0] == '0' && s[1] == 'x'))
		s += 2, base = 16;
	else if (base == 0 && s[0] == '0')
		s++, base = 8;
	else if (base == 0)
		base = 10;

	// digits
	while (1) {
		int dig;

		if (*s >= '0' && *s <= '9')
			dig = *s - '0';
		else if (*s >= 'a' && *s <= 'z')
			dig = *s - 'a' + 10;
		else if (*s >= 'A' && *s <= 'Z')
			dig = *s - 'A' + 10;
		else
			break;
		if (dig >= base)
			break;
		s++, val = (val * base) + dig;
		// we don't properly detect overflow!
	}

	if (endptr)
		*endptr = (char *) s;
	return (neg ? -val : val);
}