Use in-house CRC32 computation for boot sector

1 files changed, 22 insertions, 0 deletions

diff --git a/octedit/crc32.c b/octedit/crc32.c
new file mode 100644
index 0000000..175ab50
--- /dev/null
+++ b/octedit/crc32.c
@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <stdint.h>
+
+#define DATA_LEN 252
+#define DIVISOR 0x04C11DB7
+
+int main() {
+  uint8_t data[DATA_LEN];
+  read(STDIN_FILENO, data, DATA_LEN);
+  uint32_t crc = 0xFFFFFFFF;
+  for (size_t i = 0; i < DATA_LEN; i++) {
+    crc ^= data[i] << 24;
+    for (uint8_t j = 0; j < 8; j++) {
+      uint8_t nskip = crc >> 31;
+      crc <<= 1;
+      if (nskip) crc ^= DIVISOR;
+    }
+  }
+  write(STDOUT_FILENO, (uint8_t *) &crc, 4);
+  return 0;
+}