9b0a1dadc3
Fix off-by-one error in 64bit reciprocal division when divisor is 32bit.
Caught with the unit test:
RTE>>reciprocal_division
Validating unsigned 32bit division.
Validating unsigned 64bit division.
Validating unsigned 64bit division with 32bit divisor.
Division failed, 16983222950483802557/819 = expected 20736535959076681
result 20736535959076682
Validating division by power of 2.
Test Failed
Fixes: 6d45659eac ("eal: add u64-bit variant for reciprocal divide")
Cc: stable@dpdk.org
Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
153 lines
3.9 KiB
C
153 lines
3.9 KiB
C
/* 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"
|
|
|
|
struct rte_reciprocal rte_reciprocal_value(uint32_t d)
|
|
{
|
|
struct rte_reciprocal R;
|
|
uint64_t m;
|
|
int l;
|
|
|
|
l = rte_fls_u32(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;
|
|
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;
|
|
}
|