From: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
Date: Fri, 26 Jan 2018 05:04:50 +0000 (+0530)
Subject: eal: add u64-bit variant for reciprocal divide
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=6d45659eacb8;p=dpdk.git

eal: add u64-bit variant for reciprocal divide

Currently, rte_reciprocal only supports unsigned 32bit divisors. This
commit adds support for unsigned 64bit divisors.

Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
---

diff --git a/lib/librte_eal/common/include/rte_reciprocal.h b/lib/librte_eal/common/include/rte_reciprocal.h
index 5e21f096fa..3492c73baf 100644
--- a/lib/librte_eal/common/include/rte_reciprocal.h
+++ b/lib/librte_eal/common/include/rte_reciprocal.h
@@ -1,3 +1,6 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2017 Cavium, Inc
+ */
 /*
  * Reciprocal divide
  *
@@ -29,6 +32,11 @@ struct rte_reciprocal {
 	uint8_t sh1, sh2;
 };
 
+struct rte_reciprocal_u64 {
+	uint64_t m;
+	uint8_t sh1, sh2;
+};
+
 static inline uint32_t rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R)
 {
 	uint32_t t = (uint32_t)(((uint64_t)a * R.m) >> 32);
@@ -36,6 +44,47 @@ static inline uint32_t rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R
 	return (t + ((a - t) >> R.sh1)) >> R.sh2;
 }
 
+static __rte_always_inline uint64_t
+mullhi_u64(uint64_t x, uint64_t y)
+{
+#ifdef __SIZEOF_INT128__
+	__uint128_t xl = x;
+	__uint128_t rl = xl * y;
+
+	return (rl >> 64);
+#else
+	uint64_t u0, u1, v0, v1, k, t;
+	uint64_t w1, w2;
+	uint64_t whi;
+
+	u1 = x >> 32; u0 = x & 0xFFFFFFFF;
+	v1 = y >> 32; v0 = y & 0xFFFFFFFF;
+
+	t = u0*v0;
+	k = t >> 32;
+
+	t = u1*v0 + k;
+	w1 = t & 0xFFFFFFFF;
+	w2 = t >> 32;
+
+	t = u0*v1 + w1;
+	k = t >> 32;
+
+	whi = u1*v1 + w2 + k;
+
+	return whi;
+#endif
+}
+
+static __rte_always_inline uint64_t
+rte_reciprocal_divide_u64(uint64_t a, struct rte_reciprocal_u64 *R)
+{
+	uint64_t t = mullhi_u64(a, R->m);
+
+	return (t + ((a - t) >> R->sh1)) >> R->sh2;
+}
+
 struct rte_reciprocal rte_reciprocal_value(uint32_t d);
+struct rte_reciprocal_u64 rte_reciprocal_value_u64(uint64_t d);
 
 #endif /* _RTE_RECIPROCAL_H_ */
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;
+}
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index a179f5e8d8..ce299d3a82 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -207,7 +207,9 @@ DPDK_18.02 {
 	rte_hypervisor_get_name;
 	rte_vfio_clear_group;
 	rte_reciprocal_value;
-} DPDK_17.11;
+	rte_reciprocal_value_u64;
+
+}  DPDK_17.11;
 
 EXPERIMENTAL {
 	global: