xref: /Linux-v5.4/arch/x86/boot/string.c

// SPDX-License-Identifier: GPL-2.0-only
/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright (C) 1991, 1992 Linus Torvalds
 *   Copyright 2007 rPath, Inc. - All Rights Reserved
 *
 * ----------------------------------------------------------------------- */

/*
 * Very basic string functions
 */

#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/limits.h>
#include <asm/asm.h>
#include "ctype.h"
#include "string.h"

#define KSTRTOX_OVERFLOW       (1U << 31)

/*
 * Undef these macros so that the functions that we provide
 * here will have the correct names regardless of how string.h
 * may have chosen to #define them.
 */
#undef memcpy
#undef memset
#undef memcmp

int memcmp(const void *s1, const void *s2, size_t len)
{
	bool diff;
	asm("repe; cmpsb" CC_SET(nz)
	    : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len));
	return diff;
}

/*
 * Clang may lower `memcmp == 0` to `bcmp == 0`.
 */
int bcmp(const void *s1, const void *s2, size_t len)
{
	return memcmp(s1, s2, len);
}

int strcmp(const char *str1, const char *str2)
{
	const unsigned char *s1 = (const unsigned char *)str1;
	const unsigned char *s2 = (const unsigned char *)str2;
	int delta = 0;

	while (*s1 || *s2) {
		delta = *s1 - *s2;
		if (delta)
			return delta;
		s1++;
		s2++;
	}
	return 0;
}

int strncmp(const char *cs, const char *ct, size_t count)
{
	unsigned char c1, c2;

	while (count) {
		c1 = *cs++;
		c2 = *ct++;
		if (c1 != c2)
			return c1 < c2 ? -1 : 1;
		if (!c1)
			break;
		count--;
	}
	return 0;
}

size_t strnlen(const char *s, size_t maxlen)
{
	const char *es = s;
	while (*es && maxlen) {
		es++;
		maxlen--;
	}

	return (es - s);
}

unsigned int atou(const char *s)
{
	unsigned int i = 0;
	while (isdigit(*s))
		i = i * 10 + (*s++ - '0');
	return i;
}

/* Works only for digits and letters, but small and fast */
#define TOLOWER(x) ((x) | 0x20)

static unsigned int simple_guess_base(const char *cp)
{
	if (cp[0] == '0') {
		if (TOLOWER(cp[1]) == 'x' && isxdigit(cp[2]))
			return 16;
		else
			return 8;
	} else {
		return 10;
	}
}

/**
 * simple_strtoull - convert a string to an unsigned long long
 * @cp: The start of the string
 * @endp: A pointer to the end of the parsed string will be placed here
 * @base: The number base to use
 */

unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)
{
	unsigned long long result = 0;

	if (!base)
		base = simple_guess_base(cp);

	if (base == 16 && cp[0] == '0' && TOLOWER(cp[1]) == 'x')
		cp += 2;

	while (isxdigit(*cp)) {
		unsigned int value;

		value = isdigit(*cp) ? *cp - '0' : TOLOWER(*cp) - 'a' + 10;
		if (value >= base)
			break;
		result = result * base + value;
		cp++;
	}
	if (endp)
		*endp = (char *)cp;

	return result;
}

long simple_strtol(const char *cp, char **endp, unsigned int base)
{
	if (*cp == '-')
		return -simple_strtoull(cp + 1, endp, base);

	return simple_strtoull(cp, endp, base);
}

/**
 * strlen - Find the length of a string
 * @s: The string to be sized
 */
size_t strlen(const char *s)
{
	const char *sc;

	for (sc = s; *sc != '\0'; ++sc)
		/* nothing */;
	return sc - s;
}

/**
 * strstr - Find the first substring in a %NUL terminated string
 * @s1: The string to be searched
 * @s2: The string to search for
 */
char *strstr(const char *s1, const char *s2)
{
	size_t l1, l2;

	l2 = strlen(s2);
	if (!l2)
		return (char *)s1;
	l1 = strlen(s1);
	while (l1 >= l2) {
		l1--;
		if (!memcmp(s1, s2, l2))
			return (char *)s1;
		s1++;
	}
	return NULL;
}

/**
 * strchr - Find the first occurrence of the character c in the string s.
 * @s: the string to be searched
 * @c: the character to search for
 */
char *strchr(const char *s, int c)
{
	while (*s != (char)c)
		if (*s++ == '\0')
			return NULL;
	return (char *)s;
}

static inline u64 __div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
{
	union {
		u64 v64;
		u32 v32[2];
	} d = { dividend };
	u32 upper;

	upper = d.v32[1];
	d.v32[1] = 0;
	if (upper >= divisor) {
		d.v32[1] = upper / divisor;
		upper %= divisor;
	}
	asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
		"rm" (divisor), "0" (d.v32[0]), "1" (upper));
	return d.v64;
}

static inline u64 __div_u64(u64 dividend, u32 divisor)
{
	u32 remainder;

	return __div_u64_rem(dividend, divisor, &remainder);
}

static inline char _tolower(const char c)
{
	return c | 0x20;
}

static const char *_parse_integer_fixup_radix(const char *s, unsigned int *base)
{
	if (*base == 0) {
		if (s[0] == '0') {
			if (_tolower(s[1]) == 'x' && isxdigit(s[2]))
				*base = 16;
			else
				*base = 8;
		} else
			*base = 10;
	}
	if (*base == 16 && s[0] == '0' && _tolower(s[1]) == 'x')
		s += 2;
	return s;
}

/*
 * Convert non-negative integer string representation in explicitly given radix
 * to an integer.
 * Return number of characters consumed maybe or-ed with overflow bit.
 * If overflow occurs, result integer (incorrect) is still returned.
 *
 * Don't you dare use this function.
 */
static unsigned int _parse_integer(const char *s,
				   unsigned int base,
				   unsigned long long *p)
{
	unsigned long long res;
	unsigned int rv;

	res = 0;
	rv = 0;
	while (1) {
		unsigned int c = *s;
		unsigned int lc = c | 0x20; /* don't tolower() this line */
		unsigned int val;

		if ('0' <= c && c <= '9')
			val = c - '0';
		else if ('a' <= lc && lc <= 'f')
			val = lc - 'a' + 10;
		else
			break;

		if (val >= base)
			break;
		/*
		 * Check for overflow only if we are within range of
		 * it in the max base we support (16)
		 */
		if (unlikely(res & (~0ull << 60))) {
			if (res > __div_u64(ULLONG_MAX - val, base))
				rv |= KSTRTOX_OVERFLOW;
		}
		res = res * base + val;
		rv++;
		s++;
	}
	*p = res;
	return rv;
}

static int _kstrtoull(const char *s, unsigned int base, unsigned long long *res)
{
	unsigned long long _res;
	unsigned int rv;

	s = _parse_integer_fixup_radix(s, &base);
	rv = _parse_integer(s, base, &_res);
	if (rv & KSTRTOX_OVERFLOW)
		return -ERANGE;
	if (rv == 0)
		return -EINVAL;
	s += rv;
	if (*s == '\n')
		s++;
	if (*s)
		return -EINVAL;
	*res = _res;
	return 0;
}

/**
 * kstrtoull - convert a string to an unsigned long long
 * @s: The start of the string. The string must be null-terminated, and may also
 *  include a single newline before its terminating null. The first character
 *  may also be a plus sign, but not a minus sign.
 * @base: The number base to use. The maximum supported base is 16. If base is
 *  given as 0, then the base of the string is automatically detected with the
 *  conventional semantics - If it begins with 0x the number will be parsed as a
 *  hexadecimal (case insensitive), if it otherwise begins with 0, it will be
 *  parsed as an octal number. Otherwise it will be parsed as a decimal.
 * @res: Where to write the result of the conversion on success.
 *
 * Returns 0 on success, -ERANGE on overflow and -EINVAL on parsing error.
 * Used as a replacement for the obsolete simple_strtoull. Return code must
 * be checked.
 */
int kstrtoull(const char *s, unsigned int base, unsigned long long *res)
{
	if (s[0] == '+')
		s++;
	return _kstrtoull(s, base, res);
}