Initial commit: SUB-OS 64-Bit Production Monolithic Operating System with LazyBox userland suite

crypto/crc32.c

@@ -0,0 +1,35 @@
+#include <crypto/crypto.h>
+
+static uint32_t crc32_table[256];
+static bool table_computed = false;
+
+static void make_crc32_table(void) {
+    uint32_t c;
+    for (uint32_t n = 0; n < 256; n++) {
+        c = n;
+        for (int k = 0; k < 8; k++) {
+            if (c & 1) {
+                c = 0xEDB88320L ^ (c >> 1);
+            } else {
+                c = c >> 1;
+            }
+        }
+        crc32_table[n] = c;
+    }
+    table_computed = true;
+}
+
+uint32_t crc32(uint32_t crc, const void* buf, size_t size) {
+    if (!table_computed) {
+        make_crc32_table();
+    }
+
+    const uint8_t* p = (const uint8_t*)buf;
+    crc = crc ^ 0xFFFFFFFF;
+
+    while (size--) {
+        crc = crc32_table[(crc ^ *p++) & 0xFF] ^ (crc >> 8);
+    }
+
+    return crc ^ 0xFFFFFFFF;
+}