From c4a38865040111bd79458afd8a60d80dd011c3e8 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Mon, 21 Nov 2022 17:03:27 +0100
Subject: [PATCH] c: ex3: add solution

---
 c/ex3.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 c/ex3.c

diff --git a/c/ex3.c b/c/ex3.c
new file mode 100644
index 0000000..84ff9a3
--- /dev/null
+++ b/c/ex3.c
@@ -0,0 +1,32 @@
+#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]);
+    }
+}