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