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1 /* SPDX-License-Identifier: BSD-3-Clause
2 * Copyright(c) 2017 Cavium, Inc
7 * Copyright(c) Hannes Frederic Sowa
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
14 * * Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * * Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in
18 * the documentation and/or other materials provided with the
20 * * Neither the name of Intel Corporation nor the names of its
21 * contributors may be used to endorse or promote products derived
22 * from this software without specific prior written permission.
24 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
25 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
26 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
27 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
28 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
29 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
30 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
34 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
40 #include <rte_common.h>
42 #include "rte_reciprocal.h"
44 /* find largest set bit.
45 * portable and slow but does not matter for this usage.
47 static inline int fls(uint32_t x
)
51 for (b
= 31; b
>= 0; --b
) {
59 struct rte_reciprocal
rte_reciprocal_value(uint32_t d
)
61 struct rte_reciprocal R
;
66 m
= ((1ULL << 32) * ((1ULL << l
) - d
));
71 R
.sh1
= RTE_MIN(l
, 1);
72 R
.sh2
= RTE_MAX(l
- 1, 0);
78 * Code taken from Hacker's Delight:
79 * http://www.hackersdelight.org/hdcodetxt/divlu.c.txt
80 * License permits inclusion here per:
81 * http://www.hackersdelight.org/permissions.htm
84 divide_128_div_64_to_64(uint64_t u1
, uint64_t u0
, uint64_t v
, uint64_t *r
)
86 const uint64_t b
= (1ULL << 32); /* Number base (16 bits). */
87 uint64_t un1
, un0
, /* Norm. dividend LSD's. */
88 vn1
, vn0
, /* Norm. divisor digits. */
89 q1
, q0
, /* Quotient digits. */
90 un64
, un21
, un10
, /* Dividend digit pairs. */
91 rhat
; /* A remainder. */
92 int s
; /* Shift amount for norm. */
94 /* If overflow, set rem. to an impossible value. */
101 /* Count leading zeros. */
102 s
= __builtin_clzll(v
);
105 un64
= (u1
<< s
) | ((u0
>> (64 - s
)) & (-s
>> 31));
114 vn0
= v
& 0xFFFFFFFF;
117 un0
= un10
& 0xFFFFFFFF;
120 rhat
= un64
- q1
*vn1
;
122 if (q1
>= b
|| q1
*vn0
> b
*rhat
+ un1
) {
129 un21
= un64
*b
+ un1
- q1
*v
;
132 rhat
= un21
- q0
*vn1
;
134 if (q0
>= b
|| q0
*vn0
> b
*rhat
+ un0
) {
142 *r
= (un21
*b
+ un0
- q0
*v
) >> s
;
146 struct rte_reciprocal_u64
147 rte_reciprocal_value_u64(uint64_t d
)
149 struct rte_reciprocal_u64 R
;
153 l
= 63 - __builtin_clzll(d
);
155 m
= divide_128_div_64_to_64((1ULL << l
), 0, d
, NULL
) << 1;
156 m
= (1ULL << l
) - d
? m
+ 2 : 1;
159 R
.sh1
= l
> 1 ? 1 : l
;
160 R
.sh2
= (l
> 0) ? l
: 0;
161 R
.sh2
-= R
.sh2
&& (m
== 1) ? 1 : 0;