common.c

#include "common.h"

extern void putchar(char ch);

void printf(const char *fmt, ...)
{
	va_list vargs;
	va_start(vargs, fmt);

	while(*fmt)
	{
		if(*fmt == '%')
		{
			fmt++;
			switch(*fmt)
			{
				case '\0':
					putchar('%');
					goto end;
				case '%':
					putchar('%');
					goto end;
				case 'c':
					{
					int c = va_arg(vargs, int);
					putchar(c);
					break;
					}
				case 's':{
					const char *s = va_arg(vargs, const char *);
			       		while(*s)
					{
							putchar(*s);
							s++;
					}
					break;		
				}
				case 'd':{
					int value = va_arg(vargs, int);
					if(value < 0){
						putchar('-');
						value = -value;
					}

					int divisor = 1;
				 	while(value / divisor > 9)
						divisor *= 10;
					 
					while(divisor > 0)
					{
						putchar('0' + value / divisor);
						value %= divisor;
						divisor /= 10;
					}
					break;
				}
				case 'x':
				case 'X': {
					int value = va_arg(vargs, int);
			       		for(int i = 7; i >= 0; i--)
					{
						int nibble = (value >> (i * 4)) & 0xF;
						if(*fmt == 'x')
							putchar("0123456789abcdef"[nibble]);
						if(*fmt == 'X')
							putchar("0123456789ABCDEF"[nibble]);
					}
				}

			}
		} else{
			putchar(*fmt);
		}
		fmt++;	
	}
end:
	va_end(vargs);
}

void *memcpy(void *dst, const void *src, size_t n)
{
	uint8_t *d = (uint8_t *)dst;
	const uint8_t *s = (const uint8_t *)src;
	while(n--)
		*d++ = *s++;
	return dst;
}

void *memset(void *buf, char c, size_t n)
{
	uint8_t *p = (uint8_t *)buf;
	while(n--)
		*p++ = c;
	return buf;
}

char *strcpy(char *dst, const char *src)
{
	char *d = dst;
	while(*src)
		*d++ = *src++;
	*d = '\0';
	return dst;
}

errno_t strcpy_s(char *dst, size_t dstsz, const char *src)
{
	if(dstsz > sizeof(dst))
		return -1;
	char *d = dst;
	while(dstsz--)
		*d++ = *src++;
	*d = '\0';
	return 0;
}

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