Add crc32 combination code from pigz

Author: rhpvorderman

src/isal/crc32_combine.h

@@ -0,0 +1,87 @@
+/* pigz.c -- parallel implementation of gzip
+ * Copyright (C) 2007-2023 Mark Adler
+ * Version 2.8  19 Aug 2023  Mark Adler
+ */
+
+/*
+  This software is provided 'as-is', without any express or implied
+  warranty. In no event will the author be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Mark Adler
+  [email protected]
+
+ */
+
+/* 
+Alterations from original:
+- typedef for crc_t
+- local declarations replaced with static inline
+- g.block selector in crc32_comb removed
+*/
+
+#include <stdint.h>
+#include <stddef.h>
+
+typedef uint32_t crc_t;
+
+// CRC-32 polynomial, reflected.
+#define POLY 0xedb88320
+
+// Return a(x) multiplied by b(x) modulo p(x), where p(x) is the CRC
+// polynomial, reflected. For speed, this requires that a not be zero.
+static inline crc_t multmodp(crc_t a, crc_t b) {
+    crc_t m = (crc_t)1 << 31;
+    crc_t p = 0;
+    for (;;) {
+        if (a & m) {
+            p ^= b;
+            if ((a & (m - 1)) == 0)
+                break;
+        }
+        m >>= 1;
+        b = b & 1 ? (b >> 1) ^ POLY : b >> 1;
+    }
+    return p;
+}
+
+// Table of x^2^n modulo p(x).
+static inline const crc_t x2n_table[] = {
+    0x40000000, 0x20000000, 0x08000000, 0x00800000, 0x00008000,
+    0xedb88320, 0xb1e6b092, 0xa06a2517, 0xed627dae, 0x88d14467,
+    0xd7bbfe6a, 0xec447f11, 0x8e7ea170, 0x6427800e, 0x4d47bae0,
+    0x09fe548f, 0x83852d0f, 0x30362f1a, 0x7b5a9cc3, 0x31fec169,
+    0x9fec022a, 0x6c8dedc4, 0x15d6874d, 0x5fde7a4e, 0xbad90e37,
+    0x2e4e5eef, 0x4eaba214, 0xa8a472c0, 0x429a969e, 0x148d302a,
+    0xc40ba6d0, 0xc4e22c3c};
+
+// Return x^(n*2^k) modulo p(x).
+static inline crc_t x2nmodp(size_t n, unsigned k) {
+    crc_t p = (crc_t)1 << 31;       // x^0 == 1
+    while (n) {
+        if (n & 1)
+            p = multmodp(x2n_table[k & 31], p);
+        n >>= 1;
+        k++;
+    }
+    return p;
+}
+
+// This uses the pre-computed g.shift value most of the time. Only the last
+// combination requires a new x2nmodp() calculation.
+static inline unsigned long crc32_comb(unsigned long crc1, unsigned long crc2,
+                                       size_t len2) {
+    return multmodp(x2nmodp(len2, 3), crc1) ^ crc2;
+}