X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=lib%2Flibrte_eal%2Fcommon%2Frte_reciprocal.c;h=d81b11db6dd21d217c7f5bcdd42402b408ded8e8;hb=af4f09f28294fac762ff413fbf14b48c42c128fd;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..d81b11db6d 100644
--- a/lib/librte_eal/common/rte_reciprocal.c
+++ b/lib/librte_eal/common/rte_reciprocal.c
@@ -1,3 +1,6 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2017 Cavium, Inc
+ */
 /*-
  *   BSD LICENSE
  *
@@ -70,3 +73,92 @@ 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;
+	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;
+}