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/* SPDX-License-Identifier: BSD-3-Clause
* Copyright(c) 2017 Cavium, Inc
* Copyright(c) Hannes Frederic Sowa
* All rights reserved.
*/
#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;
}
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