1 files changed, 62 insertions, 0 deletions
diff --git a/crc32loop.c b/crc32loop.c
new file mode 100644
index 0000000..371bc96
--- /dev/null
+++ b/crc32loop.c
@@ -0,0 +1,62 @@
+#include <linux/kernel.h>
+
+enum poolinfo {
+	POOL_WORDS = 128,
+	POOL_WORDMASK = POOL_WORDS - 1,
+	POOL_BITS = POOL_WORDS * sizeof(u32) * 8,
+
+	/* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */
+	POOL_TAP1 = 104,
+	POOL_TAP2 = 76,
+	POOL_TAP3 = 51,
+	POOL_TAP4 = 25,
+	POOL_TAP5 = 1,
+};
+
+static u32 input_pool_data[POOL_WORDS];
+
+static struct {
+	u16 add_ptr;
+	u16 input_rotate;
+} input_pool = { 0 };
+
+void mix_crc32loop(const void *in, int nbytes)
+{
+	unsigned long i, j;
+	int input_rotate;
+	const u8 *bytes = in;
+	u32 w;
+
+	input_rotate = input_pool.input_rotate;
+	i = input_pool.add_ptr;
+
+	/* mix one byte at a time to simplify size handling and churn faster */
+	while (nbytes--) {
+		w = rol32(*bytes++, input_rotate);
+		i = (i - 1) & POOL_WORDMASK;
+
+		/* XOR in the various taps */
+		w ^= input_pool_data[i];
+		w ^= input_pool_data[(i + POOL_TAP1) & POOL_WORDMASK];
+		w ^= input_pool_data[(i + POOL_TAP2) & POOL_WORDMASK];
+		w ^= input_pool_data[(i + POOL_TAP3) & POOL_WORDMASK];
+		w ^= input_pool_data[(i + POOL_TAP4) & POOL_WORDMASK];
+		w ^= input_pool_data[(i + POOL_TAP5) & POOL_WORDMASK];
+
+		/* Mix the result back in with a twist */
+		for (j = 0; j < 3; ++j)
+			w = (w >> 1) ^ (0xedb88320 & -(w & 1));
+		input_pool_data[i] = w;
+
+		/*
+		 * Normally, we add 7 bits of rotation to the pool.
+		 * At the beginning of the pool, add an extra 7 bits
+		 * rotation, so that successive passes spread the
+		 * input bits across the pool evenly.
+		 */
+		input_rotate = (input_rotate + (i ? 7 : 14)) & 31;
+	}
+
+	input_pool.input_rotate = input_rotate;
+	input_pool.add_ptr = i;
+}