initial code repo

[stor4nfv.git] / src / ceph / src / common / crc32c_ppc_fast_zero_asm.S

diff --git a/src/ceph/src/common/crc32c_ppc_fast_zero_asm.S b/src/ceph/src/common/crc32c_ppc_fast_zero_asm.S
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index 0000000..a53df1d
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+++ b/src/ceph/src/common/crc32c_ppc_fast_zero_asm.S
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+/*
+ * Use the fixed point version of Barrett reduction to compute a mod n
+ * over GF(2) for given n using POWER8 instructions. We use k = 32.
+ *
+ * http://en.wikipedia.org/wiki/Barrett_reduction
+ *
+ * Copyright (C) 2015 Anton Blanchard <anton@au.ibm.com>, IBM
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of either:
+ *
+ *  a) the GNU General Public License as published by the Free Software
+ *     Foundation; either version 2 of the License, or (at your option)
+ *     any later version, or
+ *  b) the Apache License, Version 2.0
+ */
+#include <ppc-asm.h>
+#include "common/ppc-opcode.h"
+
+#undef toc
+
+#ifndef r1
+#define r1 1
+#endif
+
+#ifndef r2
+#define r2 2
+#endif
+
+       .section        .data
+.balign 16
+
+.barrett_fz_constants:
+       /* Barrett constant m - (4^32)/n */
+       .octa 0x0000000000000000000000011f91caf6        /* x^64 div p(x) */
+       /* Barrett constant n */
+       .octa 0x0000000000000000000000011edc6f41
+
+.text
+/* unsigned int barrett_reduction(unsigned long val) */
+FUNC_START(barrett_reduction)
+       addis   r4,r2,.barrett_fz_constants@toc@ha
+       addi    r4,r4,.barrett_fz_constants@toc@l
+
+       li      r5,16
+       vxor    v1,v1,v1        /* zero v1 */
+
+       /* Get a into v0 */
+       MTVRD(v0, r3)
+       vsldoi  v0,v1,v0,8      /* shift into bottom 64 bits, this is a */
+
+       /* Load constants */
+       lvx     v2,0,r4         /* m */
+       lvx     v3,r5,r4        /* n */
+
+       /*
+        * Now for the actual algorithm. The idea is to calculate q,
+        * the multiple of our polynomial that we need to subtract. By
+        * doing the computation 2x bits higher (ie 64 bits) and shifting the
+        * result back down 2x bits, we round down to the nearest multiple.
+        */
+       VPMSUMD(v4,v0,v2)       /* ma */
+       vsldoi  v4,v1,v4,8      /* q = floor(ma/(2^64)) */
+       VPMSUMD(v4,v4,v3)       /* qn */
+       vxor    v0,v0,v4        /* a - qn, subtraction is xor in GF(2) */
+
+       /*
+        * Get the result into r3. We need to shift it left 8 bytes:
+        * V0 [ 0 1 2 X ]
+        * V0 [ 0 X 2 3 ]
+        */
+       vsldoi  v0,v0,v1,8      /* shift result into top 64 bits of v0 */
+       MFVRD(r3, v0)
+
+       blr
+FUNC_END(barrett_reduction)
+