Imported Upstream version 16.04

[deb_dpdk.git] / lib / librte_sched / rte_reciprocal.h

diff --git a/lib/librte_sched/rte_reciprocal.h b/lib/librte_sched/rte_reciprocal.h
new file mode 100644 (file)
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+++ b/lib/librte_sched/rte_reciprocal.h
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+/*
+ * 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_ */