X-Git-Url: http://v3vee.org/palacios/gitweb/gitweb.cgi?p=palacios.git;a=blobdiff_plain;f=geekos%2Fsrc%2Fgeekos%2Fcrc32.c;fp=geekos%2Fsrc%2Fgeekos%2Fcrc32.c;h=a349badc2ceb90ce4363010350fe15524f5c2d8c;hp=0000000000000000000000000000000000000000;hb=ddc16b0737cf58f7aa90a69c6652cdf4090aec51;hpb=626595465a2c6987606a6bc697df65130ad8c2d3

diff --git a/geekos/src/geekos/crc32.c b/geekos/src/geekos/crc32.c
new file mode 100644
index 0000000..a349bad
--- /dev/null
+++ b/geekos/src/geekos/crc32.c
@@ -0,0 +1,53 @@
+/* Copyright abandoned; this code is in the public domain. */
+/* Provided to GNUnet by peter@horizon.com */
+
+/*
+ * Adapted for GeekOS by David Hovemeyer
+ * Code downloaded from OVM (http://www.ovmj.org)
+ */
+
+#include <geekos/crc32.h>
+#include <geekos/kassert.h>
+#include <geekos/serial.h>
+#include <geekos/debug.h>
+
+#define POLYNOMIAL (ulong_t)0xedb88320
+static ulong_t crc_table[256];
+
+/*
+ * This routine writes each crc_table entry exactly once,
+ * with the correct final value.  Thus, it is safe to call
+ * even on a table that someone else is using concurrently.
+ */
+void Init_CRC32(void) {
+  unsigned int i, j;
+  ulong_t h = 1;
+  PrintBoth("Initializing CRC32\n");
+  crc_table[0] = 0;
+  for (i = 128; i; i >>= 1) {
+    h = (h >> 1) ^ ((h & 1) ? POLYNOMIAL : 0);
+    /* h is now crc_table[i] */
+    for (j = 0; j < 256; j += 2*i)
+      crc_table[i+j] = crc_table[j] ^ h;
+  }
+}
+
+/*
+ * This computes the standard preset and inverted CRC, as used
+ * by most networking standards.  Start by passing in an initial
+ * chaining value of 0, and then pass in the return value from the
+ * previous crc32() call.  The final return value is the CRC.
+ * Note that this is a little-endian CRC, which is best used with
+ * data transmitted lsbit-first, and it should, itself, be appended
+ * to data in little-endian byte and bit order to preserve the
+ * property of detecting all burst errors of length 32 bits or less.
+ */
+ulong_t crc32(ulong_t crc, char const *buf, size_t len) {
+  KASSERT(crc_table[255] != 0);
+  crc ^= 0xffffffff;
+  while (len--)
+    crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
+  return crc ^ 0xffffffff;
+}
+
+/* end of crc32.c */