101 lines
2.2 KiB
C
101 lines
2.2 KiB
C
#include "common.h"
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void putchar(char ch);
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void printf(const char *fmt, ...) {
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va_list vargs;
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va_start(vargs, fmt);
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while (*fmt) {
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if (*fmt == '%') {
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fmt++; // Skip '%'
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switch (*fmt) { // Read the next character
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case '\0': // '%' at the end of the format string
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putchar('%');
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goto end;
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case '%': // Print '%'
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putchar('%');
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break;
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case 's': { // Print a NULL-termintated string
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const char *s = va_arg(vargs, const char *);
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while (*s) {
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putchar(*s);
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s++;
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}
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break;
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}
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case 'd': { // Print an integer in decimal
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int value = va_arg(vargs, int);
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unsigned magnitude = value;
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if (value < 0) {
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putchar('-');
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magnitude = -magnitude;
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}
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unsigned divisor = 1;
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while (magnitude / divisor > 9)
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divisor *= 10;
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while (divisor > 0) {
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putchar('0' + magnitude / divisor);
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magnitude %= divisor;
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divisor /= 10;
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}
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break;
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}
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case 'x': { // Print an integer in hexademical
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unsigned value = va_arg(vargs, unsigned);
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for (int i = 7; i >= 0; i--) {
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unsigned nibble = (value >> (i * 4)) & 0xf;
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putchar("0123456789abcdef"[nibble]);
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}
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}
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}
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} else {
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putchar(*fmt);
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}
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fmt++;
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}
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end:
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va_end(vargs);
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}
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void *memcpy(void *dst, const void *src, size_t n) {
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uint8_t *d = (uint8_t *) dst;
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const uint8_t *s = (const uint8_t *) src;
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while (n--)
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*d++ = *s++;
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return dst;
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}
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void *memset(void *buf, char c, size_t n) {
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uint8_t *p = (uint8_t *) buf;
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while (n--)
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*p++ = c;
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return buf;
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}
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char *strcpy(char *dst, const char *src) {
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char *d = dst;
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while (*src)
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*d++ = *src++;
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*d = '\0';
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return dst;
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} // The strcpy function continues copying even if
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// src is longer than the memory area of dst.
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// This can easily lead to bugs and vulnerabilities
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int strcmp(const char *s1, const char *s2) {
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while (*s1 && *s2) {
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if (*s1 != *s2)
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break;
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s1++;
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s2++;
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}
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return *(unsigned char *)s1 - *(unsigned char *)s2;
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}
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