1 files changed, 108 insertions, 0 deletions
diff --git a/crc32_comb.c b/crc32_comb.c
new file mode 100644
index 0000000..092c595
--- /dev/null
+++ b/crc32_comb.c
@@ -0,0 +1,108 @@
+/* crc32_comb.c -- compute the CRC-32 of a data stream
+ * Copyright (C) 1995-2006, 2010, 2011, 2012, 2016, 2018 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ *
+ * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
+ * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
+ * tables for updating the shift register in one step with three exclusive-ors
+ * instead of four steps with four exclusive-ors.  This results in about a
+ * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
+ */
+
+#include "zbuild.h"
+#include <inttypes.h>
+#include "deflate.h"
+#include "crc32_p.h"
+#include "crc32_comb_tbl.h"
+
+
+/* Local functions for crc concatenation */
+static uint32_t crc32_combine_(uint32_t crc1, uint32_t crc2, z_off64_t len2);
+static void crc32_combine_gen_(uint32_t *op, z_off64_t len2);
+
+/* ========================================================================= */
+static uint32_t crc32_combine_(uint32_t crc1, uint32_t crc2, z_off64_t len2) {
+    int n;
+
+    if (len2 > 0)
+        /* operator for 2^n zeros repeats every GF2_DIM n values */
+        for (n = 0; len2; n = (n + 1) % GF2_DIM, len2 >>= 1)
+            if (len2 & 1)
+                crc1 = gf2_matrix_times(crc_comb[n], crc1);
+    return crc1 ^ crc2;
+}
+
+/* ========================================================================= */
+#ifdef ZLIB_COMPAT
+unsigned long Z_EXPORT PREFIX(crc32_combine)(unsigned long crc1, unsigned long crc2, z_off_t len2) {
+    return (unsigned long)crc32_combine_((uint32_t)crc1, (uint32_t)crc2, len2);
+}
+
+unsigned long Z_EXPORT PREFIX4(crc32_combine)(unsigned long crc1, unsigned long crc2, z_off64_t len2) {
+    return (unsigned long)crc32_combine_((uint32_t)crc1, (uint32_t)crc2, len2);
+}
+#else
+uint32_t Z_EXPORT PREFIX4(crc32_combine)(uint32_t crc1, uint32_t crc2, z_off64_t len2) {
+    return crc32_combine_(crc1, crc2, len2);
+}
+#endif
+
+/* ========================================================================= */
+
+static void crc32_combine_gen_(uint32_t *op, z_off64_t len2) {
+    uint32_t row;
+    int j;
+    unsigned i;
+
+    /* if len2 is zero or negative, return the identity matrix */
+    if (len2 <= 0) {
+        row = 1;
+        for (j = 0; j < GF2_DIM; j++) {
+            op[j] = row;
+            row <<= 1;
+        }
+        return;
+    }
+
+    /* at least one bit in len2 is set -- find it, and copy the operator
+       corresponding to that position into op */
+    i = 0;
+    for (;;) {
+        if (len2 & 1) {
+            for (j = 0; j < GF2_DIM; j++)
+                op[j] = crc_comb[i][j];
+            break;
+        }
+        len2 >>= 1;
+        i = (i + 1) % GF2_DIM;
+    }
+
+    /* for each remaining bit set in len2 (if any), multiply op by the operator
+       corresponding to that position */
+    for (;;) {
+        len2 >>= 1;
+        i = (i + 1) % GF2_DIM;
+        if (len2 == 0)
+            break;
+        if (len2 & 1)
+            for (j = 0; j < GF2_DIM; j++)
+                op[j] = gf2_matrix_times(crc_comb[i], op[j]);
+    }
+}
+
+/* ========================================================================= */
+
+#ifdef ZLIB_COMPAT
+void Z_EXPORT PREFIX(crc32_combine_gen)(uint32_t *op, z_off_t len2) {
+    crc32_combine_gen_(op, len2);
+}
+#endif
+
+void Z_EXPORT PREFIX4(crc32_combine_gen)(uint32_t *op, z_off64_t len2) {
+    crc32_combine_gen_(op, len2);
+}
+
+/* ========================================================================= */
+uint32_t Z_EXPORT PREFIX(crc32_combine_op)(uint32_t crc1, uint32_t crc2, const uint32_t *op) {
+    return gf2_matrix_times(op, crc1) ^ crc2;
+}