X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=lib%2Flibrte_eal%2Fcommon%2Frte_reciprocal.c;h=42dfa44eb49ecff9904b839a9034a40d06d371bc;hb=06c7871dde01;hp=652f0237aa29db9981e330bde811a4a35787eb7d;hpb=0b037e8b02b7ced8c18a650b708f2fd6e3364d83;p=dpdk.git

diff --git a/lib/librte_eal/common/rte_reciprocal.c b/lib/librte_eal/common/rte_reciprocal.c
index 652f0237aa..42dfa44eb4 100644
--- a/lib/librte_eal/common/rte_reciprocal.c
+++ b/lib/librte_eal/common/rte_reciprocal.c
@@ -1,34 +1,7 @@
-/*-
- *   BSD LICENSE
- *
- *   Copyright(c) Hannes Frederic Sowa
- *   All rights reserved.
- *
- *   Redistribution and use in source and binary forms, with or without
- *   modification, are permitted provided that the following conditions
- *   are met:
- *
- *     * Redistributions of source code must retain the above copyright
- *       notice, this list of conditions and the following disclaimer.
- *     * Redistributions in binary form must reproduce the above copyright
- *       notice, this list of conditions and the following disclaimer in
- *       the documentation and/or other materials provided with the
- *       distribution.
- *     * Neither the name of Intel Corporation nor the names of its
- *       contributors may be used to endorse or promote products derived
- *       from this software without specific prior written permission.
- *
- *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
- *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
- *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2017 Cavium, Inc
+ * Copyright(c) Hannes Frederic Sowa
+ * All rights reserved.
  */
 
 #include <stdio.h>
@@ -38,28 +11,13 @@
 
 #include "rte_reciprocal.h"
 
-/* find largest set bit.
- * portable and slow but does not matter for this usage.
- */
-static inline int fls(uint32_t x)
-{
-	int b;
-
-	for (b = 31; b >= 0; --b) {
-		if (x & (1u << b))
-			return b + 1;
-	}
-
-	return 0;
-}
-
 struct rte_reciprocal rte_reciprocal_value(uint32_t d)
 {
 	struct rte_reciprocal R;
 	uint64_t m;
 	int l;
 
-	l = fls(d - 1);
+	l = rte_fls_u32(d - 1);
 	m = ((1ULL << 32) * ((1ULL << l) - d));
 	m /= d;
 
@@ -70,3 +28,95 @@ struct rte_reciprocal rte_reciprocal_value(uint32_t d)
 
 	return R;
 }
+
+/*
+ * Code taken from Hacker's Delight:
+ * http://www.hackersdelight.org/hdcodetxt/divlu.c.txt
+ * License permits inclusion here per:
+ * http://www.hackersdelight.org/permissions.htm
+ */
+static uint64_t
+divide_128_div_64_to_64(uint64_t u1, uint64_t u0, uint64_t v, uint64_t *r)
+{
+	const uint64_t b = (1ULL << 32); /* Number base (16 bits). */
+	uint64_t un1, un0,           /* Norm. dividend LSD's. */
+		 vn1, vn0,           /* Norm. divisor digits. */
+		 q1, q0,             /* Quotient digits. */
+		 un64, un21, un10,   /* Dividend digit pairs. */
+		 rhat;               /* A remainder. */
+	int s;                       /* Shift amount for norm. */
+
+	/* If overflow, set rem. to an impossible value. */
+	if (u1 >= v) {
+		if (r != NULL)
+			*r = (uint64_t) -1;
+		return (uint64_t) -1;
+	}
+
+	/* Count leading zeros. */
+	s = __builtin_clzll(v);
+	if (s > 0) {
+		v = v << s;
+		un64 = (u1 << s) | ((u0 >> (64 - s)) & (-s >> 31));
+		un10 = u0 << s;
+	} else {
+
+		un64 = u1 | u0;
+		un10 = u0;
+	}
+
+	vn1 = v >> 32;
+	vn0 = v & 0xFFFFFFFF;
+
+	un1 = un10 >> 32;
+	un0 = un10 & 0xFFFFFFFF;
+
+	q1 = un64/vn1;
+	rhat = un64 - q1*vn1;
+again1:
+	if (q1 >= b || q1*vn0 > b*rhat + un1) {
+		q1 = q1 - 1;
+		rhat = rhat + vn1;
+		if (rhat < b)
+			goto again1;
+	}
+
+	un21 = un64*b + un1 - q1*v;
+
+	q0 = un21/vn1;
+	rhat = un21 - q0*vn1;
+again2:
+	if (q0 >= b || q0*vn0 > b*rhat + un0) {
+		q0 = q0 - 1;
+		rhat = rhat + vn1;
+		if (rhat < b)
+			goto again2;
+	}
+
+	if (r != NULL)
+		*r = (un21*b + un0 - q0*v) >> s;
+	return q1*b + q0;
+}
+
+struct rte_reciprocal_u64
+rte_reciprocal_value_u64(uint64_t d)
+{
+	struct rte_reciprocal_u64 R;
+	uint64_t m;
+	uint64_t r;
+	int l;
+
+	l = 63 - __builtin_clzll(d);
+
+	m = divide_128_div_64_to_64((1ULL << l), 0, d, &r) << 1;
+	if (r << 1 < r || r << 1 >= d)
+		m++;
+	m = (1ULL << l) - d ? m + 1 : 1;
+	R.m = m;
+
+	R.sh1 = l > 1 ? 1 : l;
+	R.sh2 = (l > 0) ? l : 0;
+	R.sh2 -= R.sh2 && (m == 1) ? 1 : 0;
+
+	return R;
+}