aboutsummaryrefslogtreecommitdiffstats
path: root/lib/librte_sched/rte_reciprocal.h
diff options
context:
space:
mode:
authorC.J. Collier <cjcollier@linuxfoundation.org>2016-06-14 07:54:47 -0700
committerC.J. Collier <cjcollier@linuxfoundation.org>2016-06-14 07:55:43 -0700
commit5129044dce1f85ce4950f31bcf90f3886466f06a (patch)
tree1c6269614c0c15ffef8451c58ae8f8b30a1bc804 /lib/librte_sched/rte_reciprocal.h
parente04be89c2409570e0055b2cda60bd11395bb93b0 (diff)
Imported upstream release 16.04
* gbp import-orig ../dpdk-16.04.tar.xz Change-Id: Iac2196db782ba322f6974d8a752acc34ce5024c3 Signed-off-by: C.J. Collier <cjcollier@linuxfoundation.org>
Diffstat (limited to 'lib/librte_sched/rte_reciprocal.h')
-rw-r--r--lib/librte_sched/rte_reciprocal.h39
1 files changed, 39 insertions, 0 deletions
diff --git a/lib/librte_sched/rte_reciprocal.h b/lib/librte_sched/rte_reciprocal.h
new file mode 100644
index 00000000..abd15251
--- /dev/null
+++ b/lib/librte_sched/rte_reciprocal.h
@@ -0,0 +1,39 @@
+/*
+ * Reciprocal divide
+ *
+ * Used with permission from original authors
+ * Hannes Frederic Sowa and Daniel Borkmann
+ *
+ * This algorithm is based on the paper "Division by Invariant
+ * Integers Using Multiplication" by Torbjörn Granlund and Peter
+ * L. Montgomery.
+ *
+ * The assembler implementation from Agner Fog, which this code is
+ * based on, can be found here:
+ * http://www.agner.org/optimize/asmlib.zip
+ *
+ * This optimization for A/B is helpful if the divisor B is mostly
+ * runtime invariant. The reciprocal of B is calculated in the
+ * slow-path with reciprocal_value(). The fast-path can then just use
+ * a much faster multiplication operation with a variable dividend A
+ * to calculate the division A/B.
+ */
+
+#ifndef _RTE_RECIPROCAL_H_
+#define _RTE_RECIPROCAL_H_
+
+struct rte_reciprocal {
+ uint32_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);
+
+ return (t + ((a - t) >> R.sh1)) >> R.sh2;
+}
+
+struct rte_reciprocal rte_reciprocal_value(uint32_t d);
+
+#endif /* _RTE_RECIPROCAL_H_ */