#include <string.h>

void *memchr(const void *s, int c, size_t n) {
  unsigned char *p = (unsigned char*) s;
  while(n--) {
    if(*p != (unsigned char) c) {
      p++;
    } else {
      return p;
    }
  }
  return 0;
}

int memcmp(const void *s1, const void *s2, size_t n) {
  const unsigned char *p1 = (const unsigned char*) s1;
  const unsigned char *p2 = (const unsigned char*) s2;
  while(n--) {
    if(*p1 != *p2) {
      return *p1 - *p2;
    } else {
      p1++, p2++;
    }
  }
  return 0;
}

void *memcpy(void *dest, const void *src, size_t n) {
  char *dp = (char*) dest;
  const char *sp = (const char*) src;
  while(n--) *dp++ = *sp++;
  return dest;
}

void *memmove(void *dest, const void *src, size_t n) {
  unsigned char tmp[n];
  memcpy(tmp, src, n);
  memcpy(dest, tmp, n);
  return dest;
}

void *memset(void *s, int c, size_t n) {
  unsigned char *p = (unsigned char*) s;
  while(n--) *p++ = (unsigned char) c;
  return s;
}

size_t strlen(const char *str) {
  const char *s;
  for(s = str; *s; ++s) {}
  return (s - str);
}

char *strcat(char *dest, const char *src) {
  size_t dest_len = strlen(dest);
  size_t i;

  for(i = 0; src[i] != '\0'; i++) {
    dest[dest_len + i] = src[i];
  }
  dest[dest_len + i] = '\0';
  return dest;
}

char *strncat(char *dest, const char *src, size_t n) {
  size_t dest_len = strlen(dest);
  size_t i;

  for(i = 0; i < n && src[i] != '\0'; i++) {
    dest[dest_len + i] = src[i];
  }
  dest[dest_len + i] = '\0';
  return dest;
}

char *strchr(const char *s, int c) {
  while(*s != (char) c) {
    if(!*s++) return 0;
  }
  return (char*) s;
}

char *strrchr(char *s, int c) {
  char *ret = 0;
  do {
    if(*s == (char) c) ret = s;
  } while(*s++);
  return ret;
}

int strcmp(const char *s1, const char *s2) {
  while(*s1 && (*s1 == *s2)) s1++, s2++;
  return *(const unsigned char*) s1 - *(const unsigned char*) s2;
}

int strncmp(const char *s1, const char *s2, size_t n) {
  while(n--) {
    if(*s1++ != *s2++) {
      return *(unsigned char*) (s1 - 1) - *(unsigned char*) (s2 - 1);
    }
  }
  return 0;
}

char *strcpy(char *dest, const char *src) {
  char *ret = dest;
  while(*dest++ = *src++);
  return ret;
}

char *strncpy(char *dest, const char *src, size_t n) {
  char *ret = dest;
  do {
    if(!n--) return ret;
  } while (*dest++ = *src++);
  while(n--) *dest++ = 0;
  return ret;
}

size_t strcspn(const char *s1, const char *s2) {
  size_t ret = 0;
  while(*s1) {
    if(strchr(s2, *s1)) {
      return ret;
    } else {
      s1++, ret++;
    }
  }
  return ret;
}

size_t strspn(const char *s1, const char *s2) {
  size_t ret = 0;
  while(*s1 && strchr(s2, *s1++)) ret++;
  return ret;
}

char *strpbrk(const char *s1, const char *s2) {
  while(*s1) {
    if(strchr(s2, *s1++)) return (char*) --s1;
  }
  return 0;
}

char *strstr(const char *s1, const char *s2) {
  size_t n = strlen(s2);
  while(*s1) {
    if(!memcmp(s1++, s2, n)) {
      return (char*) (s1 - 1);
    }
  }
  return 0;
}

char *strtok(char *str, const char *delim) {
  static char *p = 0;
  if(str) {
    p = str;
  } else if(!p) {
    return 0;
  }
  str = p + strspn(p, delim);
  p = str + strcspn(str, delim);
  if(p == str) return p = 0;
  p = *p ? *p = 0, p + 1 : 0;
  return str;
}

size_t strxfrm(char *dest, const char *src, size_t n) {
  size_t n2 = strlen(src);
  if(n > n2) strcpy(dest, src);
  return n2;
}