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authorLuca Boccassi <luca.boccassi@gmail.com>2018-02-19 11:16:57 +0000
committerLuca Boccassi <luca.boccassi@gmail.com>2018-02-19 11:17:28 +0000
commitca33590b6af032bff57d9cc70455660466a654b2 (patch)
tree0b68b090bd9b4a78a3614b62400b29279d76d553 /lib/librte_eal/common/rte_reciprocal.c
parent169a9de21e263aa6599cdc2d87a45ae158d9f509 (diff)
New upstream version 18.02upstream/18.02
Change-Id: I89ed24cb2a49b78fe5be6970b99dd46c1499fcc3 Signed-off-by: Luca Boccassi <luca.boccassi@gmail.com>
Diffstat (limited to 'lib/librte_eal/common/rte_reciprocal.c')
-rw-r--r--lib/librte_eal/common/rte_reciprocal.c164
1 files changed, 164 insertions, 0 deletions
diff --git a/lib/librte_eal/common/rte_reciprocal.c b/lib/librte_eal/common/rte_reciprocal.c
new file mode 100644
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+++ b/lib/librte_eal/common/rte_reciprocal.c
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+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2017 Cavium, Inc
+ */
+/*-
+ * 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.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+
+#include <rte_common.h>
+
+#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);
+ m = ((1ULL << 32) * ((1ULL << l) - d));
+ m /= d;
+
+ ++m;
+ R.m = m;
+ R.sh1 = RTE_MIN(l, 1);
+ R.sh2 = RTE_MAX(l - 1, 0);
+
+ 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;
+ int l;
+
+ l = 63 - __builtin_clzll(d);
+
+ m = divide_128_div_64_to_64((1ULL << l), 0, d, NULL) << 1;
+ m = (1ULL << l) - d ? m + 2 : 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;
+}