next-dlp/c/ex3.c

33 lines
801 B
C

#include <limits.h>
#include <stddef.h>
static unsigned char reverse_byte(unsigned char c) {
unsigned char res = 0;
for (size_t i = 0; i < CHAR_BIT; ++i) {
unsigned char bit = (c & (1 << i));
res |= bit << (CHAR_BIT - i - 1);
}
return res;
}
static void swap_bytes(unsigned char* lhs, unsigned char* rhs) {
unsigned char tmp = *lhs;
*lhs = *rhs;
*rhs = tmp;
}
void reverse_bytes(unsigned char* buf, size_t n) {
if (!buf || !n)
return;
// No need to worry about applying reverse_byte twice in the middle by
// mistake if done in a preliminary pass
for (size_t i = 0; i < n; ++i) {
buf[i] = reverse_byte(buf[i]);
}
for (size_t i = 0; i < ((n + 1) / 2); ++i) {
swap_bytes(&buf[i], &buf[n - 1 - i]);
}
}