MINOR: hash: add new function hash_crc32
This function will be used to perform CRC32 computations. This one wa
loosely inspired from crc32b found here, and focuses on size and speed
at the same time :
http://www.hackersdelight.org/hdcodetxt/crc.c.txt
Much faster table-based versions exist but are pointless for our usage
here, this hash already sustains gigabit speed which is far faster than
what we'd ever need. Better preserve the CPU's cache instead.
diff --git a/src/hash.c b/src/hash.c
index aa236cb..43ba11c 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -85,4 +85,23 @@
return hash;
}
+/* Small yet efficient CRC32 calculation loosely inspired from crc32b found
+ * here : http://www.hackersdelight.org/hdcodetxt/crc.c.txt
+ * The magic value represents the polynom with one bit per exponent. Much
+ * faster table-based versions exist but are pointless for our usage here,
+ * this hash already sustains gigabit speed which is far faster than what
+ * we'd ever need. Better preserve the CPU's cache instead.
+ */
+unsigned int hash_crc32(const char *key, int len)
+{
+ unsigned int hash;
+ int bit;
+ hash = ~0;
+ while (len--) {
+ hash ^= *key++;
+ for (bit = 0; bit < 8; bit++)
+ hash = (hash >> 1) ^ ((hash & 1) ? 0xedb88320 : 0);
+ }
+ return ~hash;
+}