《操作系统》的实验代码。
 
 
 
 
 

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#include <string.h>
#include <x86.h>
/* *
* strlen - calculate the length of the string @s, not including
* the terminating '\0' character.
* @s: the input string
*
* The strlen() function returns the length of string @s.
* */
size_t
strlen(const char *s) {
size_t cnt = 0;
while (*s ++ != '\0') {
cnt ++;
}
return cnt;
}
/* *
* strnlen - calculate the length of the string @s, not including
* the terminating '\0' char acter, but at most @len.
* @s: the input string
* @len: the max-length that function will scan
*
* Note that, this function looks only at the first @len characters
* at @s, and never beyond @s + @len.
*
* The return value is strlen(s), if that is less than @len, or
* @len if there is no '\0' character among the first @len characters
* pointed by @s.
* */
size_t
strnlen(const char *s, size_t len) {
size_t cnt = 0;
while (cnt < len && *s ++ != '\0') {
cnt ++;
}
return cnt;
}
/* *
* strcpy - copies the string pointed by @src into the array pointed by @dst,
* including the terminating null character.
* @dst: pointer to the destination array where the content is to be copied
* @src: string to be copied
*
* The return value is @dst.
*
* To avoid overflows, the size of array pointed by @dst should be long enough to
* contain the same string as @src (including the terminating null character), and
* should not overlap in memory with @src.
* */
char *
strcpy(char *dst, const char *src) {
#ifdef __HAVE_ARCH_STRCPY
return __strcpy(dst, src);
#else
char *p = dst;
while ((*p ++ = *src ++) != '\0')
/* nothing */;
return dst;
#endif /* __HAVE_ARCH_STRCPY */
}
/* *
* strncpy - copies the first @len characters of @src to @dst. If the end of string @src
* if found before @len characters have been copied, @dst is padded with '\0' until a
* total of @len characters have been written to it.
* @dst: pointer to the destination array where the content is to be copied
* @src: string to be copied
* @len: maximum number of characters to be copied from @src
*
* The return value is @dst
* */
char *
strncpy(char *dst, const char *src, size_t len) {
char *p = dst;
while (len > 0) {
if ((*p = *src) != '\0') {
src ++;
}
p ++, len --;
}
return dst;
}
/* *
* strcmp - compares the string @s1 and @s2
* @s1: string to be compared
* @s2: string to be compared
*
* This function starts comparing the first character of each string. If
* they are equal to each other, it continues with the following pairs until
* the characters differ or until a terminanting null-character is reached.
*
* Returns an integral value indicating the relationship between the strings:
* - A zero value indicates that both strings are equal;
* - A value greater than zero indicates that the first character that does
* not match has a greater value in @s1 than in @s2;
* - And a value less than zero indicates the opposite.
* */
int
strcmp(const char *s1, const char *s2) {
#ifdef __HAVE_ARCH_STRCMP
return __strcmp(s1, s2);
#else
while (*s1 != '\0' && *s1 == *s2) {
s1 ++, s2 ++;
}
return (int)((unsigned char)*s1 - (unsigned char)*s2);
#endif /* __HAVE_ARCH_STRCMP */
}
/* *
* strncmp - compares up to @n characters of the string @s1 to those of the string @s2
* @s1: string to be compared
* @s2: string to be compared
* @n: maximum number of characters to compare
*
* This function starts comparing the first character of each string. If
* they are equal to each other, it continues with the following pairs until
* the characters differ, until a terminating null-character is reached, or
* until @n characters match in both strings, whichever happens first.
* */
int
strncmp(const char *s1, const char *s2, size_t n) {
while (n > 0 && *s1 != '\0' && *s1 == *s2) {
n --, s1 ++, s2 ++;
}
return (n == 0) ? 0 : (int)((unsigned char)*s1 - (unsigned char)*s2);
}
/* *
* strchr - locates first occurrence of character in string
* @s: the input string
* @c: character to be located
*
* The strchr() function returns a pointer to the first occurrence of
* character in @s. If the value is not found, the function returns 'NULL'.
* */
char *
strchr(const char *s, char c) {
while (*s != '\0') {
if (*s == c) {
return (char *)s;
}
s ++;
}
return NULL;
}
/* *
* strfind - locates first occurrence of character in string
* @s: the input string
* @c: character to be located
*
* The strfind() function is like strchr() except that if @c is
* not found in @s, then it returns a pointer to the null byte at the
* end of @s, rather than 'NULL'.
* */
char *
strfind(const char *s, char c) {
while (*s != '\0') {
if (*s == c) {
break;
}
s ++;
}
return (char *)s;
}
/* *
* strtol - converts string to long integer
* @s: the input string that contains the representation of an integer number
* @endptr: reference to an object of type char *, whose value is set by the
* function to the next character in @s after the numerical value. This
* parameter can also be a null pointer, in which case it is not used.
* @base: x
*
* The function first discards as many whitespace characters as necessary until
* the first non-whitespace character is found. Then, starting from this character,
* takes as many characters as possible that are valid following a syntax that
* depends on the base parameter, and interprets them as a numerical value. Finally,
* a pointer to the first character following the integer representation in @s
* is stored in the object pointed by @endptr.
*
* If the value of base is zero, the syntax expected is similar to that of
* integer constants, which is formed by a succession of:
* - An optional plus or minus sign;
* - An optional prefix indicating octal or hexadecimal base ("0" or "0x" respectively)
* - A sequence of decimal digits (if no base prefix was specified) or either octal
* or hexadecimal digits if a specific prefix is present
*
* If the base value is between 2 and 36, the format expected for the integral number
* is a succession of the valid digits and/or letters needed to represent integers of
* the specified radix (starting from '0' and up to 'z'/'Z' for radix 36). The
* sequence may optionally be preceded by a plus or minus sign and, if base is 16,
* an optional "0x" or "0X" prefix.
*
* The strtol() function returns the converted integral number as a long int value.
* */
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);
}
/* *
* memset - sets the first @n bytes of the memory area pointed by @s
* to the specified value @c.
* @s: pointer the the memory area to fill
* @c: value to set
* @n: number of bytes to be set to the value
*
* The memset() function returns @s.
* */
void *
memset(void *s, char c, size_t n) {
#ifdef __HAVE_ARCH_MEMSET
return __memset(s, c, n);
#else
char *p = s;
while (n -- > 0) {
*p ++ = c;
}
return s;
#endif /* __HAVE_ARCH_MEMSET */
}
/* *
* memmove - copies the values of @n bytes from the location pointed by @src to
* the memory area pointed by @dst. @src and @dst are allowed to overlap.
* @dst pointer to the destination array where the content is to be copied
* @src pointer to the source of data to by copied
* @n: number of bytes to copy
*
* The memmove() function returns @dst.
* */
void *
memmove(void *dst, const void *src, size_t n) {
#ifdef __HAVE_ARCH_MEMMOVE
return __memmove(dst, src, n);
#else
const char *s = src;
char *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;
#endif /* __HAVE_ARCH_MEMMOVE */
}
/* *
* memcpy - copies the value of @n bytes from the location pointed by @src to
* the memory area pointed by @dst.
* @dst pointer to the destination array where the content is to be copied
* @src pointer to the source of data to by copied
* @n: number of bytes to copy
*
* The memcpy() returns @dst.
*
* Note that, the function does not check any terminating null character in @src,
* it always copies exactly @n bytes. To avoid overflows, the size of arrays pointed
* by both @src and @dst, should be at least @n bytes, and should not overlap
* (for overlapping memory area, memmove is a safer approach).
* */
void *
memcpy(void *dst, const void *src, size_t n) {
#ifdef __HAVE_ARCH_MEMCPY
return __memcpy(dst, src, n);
#else
const char *s = src;
char *d = dst;
while (n -- > 0) {
*d ++ = *s ++;
}
return dst;
#endif /* __HAVE_ARCH_MEMCPY */
}
/* *
* memcmp - compares two blocks of memory
* @v1: pointer to block of memory
* @v2: pointer to block of memory
* @n: number of bytes to compare
*
* The memcmp() functions returns an integral value indicating the
* relationship between the content of the memory blocks:
* - A zero value indicates that the contents of both memory blocks are equal;
* - A value greater than zero indicates that the first byte that does not
* match in both memory blocks has a greater value in @v1 than in @v2
* as if evaluated as unsigned char values;
* - And a value less than zero indicates the opposite.
* */
int
memcmp(const void *v1, const void *v2, size_t n) {
const char *s1 = (const char *)v1;
const char *s2 = (const char *)v2;
while (n -- > 0) {
if (*s1 != *s2) {
return (int)((unsigned char)*s1 - (unsigned char)*s2);
}
s1 ++, s2 ++;
}
return 0;
}