/boot/memstr.c

#include "string.h"

void *memcpy(void *dest, const void *src, size_t n) {
  char *d = (char*)dest;
  const char *s = (const char*)src;

  while (n-- > 0) {
    *d++ = *s++;
  }
  return dest;
}

void *memset(void *dest, int fill, size_t n) {
  unsigned char *d = (unsigned char*)dest;

  while (n-- > 0) {
    *d++ = (unsigned char)fill;
  }
  return dest;
}

int memcmp(const void *s1, const void *s2, size_t n) {
  unsigned char *ss1 = (unsigned char*)s1;
  unsigned char *ss2 = (unsigned char*)s2;

  while (n-- > 0) {
    if (*ss1 != *ss2) {
      return *ss1 - *ss2;
    }
    ++ss1;
    ++ss2;
  }
  return 0;
}

size_t strlen(const char *s) {
  size_t n = 0;

  while (*s++) n++;
  return n;
}

char *strcpy(char *d, const char *s) {
  char *dest = d;

  while (*d++ = *s++);
  return dest;
}

int strcmp(const char *s1, const char *s2) {
  size_t l1, l2;
  l1 = strlen(s1);
  l2 = strlen(s2);
  if (l1 < l2) {
    return -1;
  }
  if (l1 > l2) {
    return 1;
  }
  while (*s1) {
    if (*s1 != *s2) {
      return *s1 - *s2;
    }
    ++s1;
    ++s2;
  }
  return 0;
}