From 35d06ac10ca9ddb970c1355b3a44c362917a872f Mon Sep 17 00:00:00 2001
From: Kaspar Schleiser <kaspar@schleiser.de>
Date: Thu, 8 Oct 2015 13:44:47 +0200
Subject: [PATCH] sys: add header for integer division using multiplication /
shifts
---
sys/include/div.h | 112 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 112 insertions(+)
create mode 100644 sys/include/div.h
diff --git a/sys/include/div.h b/sys/include/div.h
new file mode 100644
index 0000000000..3b83aad628
--- /dev/null
+++ b/sys/include/div.h
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2015 Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @brief Provides integer division functions
+ *
+ * This header provides some integer division functions that can be used
+ * to prevent linking in compiler-generated ones, which are often larger.
+ *
+ * @file
+ * @ingroup sys_util
+ * @author Kaspar Schleiser <kaspar@schleiser.de>
+ * @{
+ */
+
+#ifndef DIV_H
+#define DIV_H
+
+#include <assert.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Integer divide val by 15625
+ *
+ * @pre val <= 16383999997
+ *
+ * @param[in] val dividend
+ * @return (val / 15625)
+ */
+static inline uint64_t div_u64_by_15625(uint64_t val)
+{
+ /* a higher value would overflow 2^64 in the multiplication that follows */
+ assert(val <= 16383999997LLU);
+
+ return (val * 0x431bde83UL) >> (12 + 32);
+}
+
+/**
+ * @brief Integer divide val by 1000000
+ *
+ * @pre val <= 1048575999808
+ *
+ * @param[in] val dividend
+ * @return (val / 1000000)
+ */
+static inline uint64_t div_u64_by_1000000(uint64_t val)
+{
+ /* a higher value would overflow 2^64 in the multiplication that follows */
+ assert(val <= 1048575999808LLU);
+
+ return div_u64_by_15625(val>>6);
+}
+
+/**
+ * @brief Divide val by (15625/512)
+ *
+ * This is used to quantize a 1MHz value to the closest 32768Hz value,
+ * e.g., for timers.
+ *
+ * The algorithm actually multiplies by 512 first, then divides by 15625,
+ * keeping the result closer to a floored floating point division.
+ *
+ * @param[in] val dividend
+ * @return (val / (15625/512))
+ */
+static inline uint32_t div_u32_by_15625div512(uint32_t val)
+{
+ return ((uint64_t)(val) * 0x431bde83ul) >> (12 + 32 - 9);
+}
+
+/**
+ * @brief Integer divide val by 10
+ *
+ * @param[in] n dividend
+ * @return (n / 10)
+ */
+static inline uint32_t div_u32_by_10(uint32_t n) {
+ uint32_t q, r;
+ q = (n >> 1) + (n >> 2);
+ q = q + (q >> 4);
+ q = q + (q >> 8);
+ q = q + (q >> 16);
+ q = q >> 3;
+ r = n - (((q << 2) + q) << 1);
+ return q + (r > 9);
+}
+
+/**
+ * @brief Modulo 10
+ *
+ * @param[in] n dividend
+ * @return (n % 10)
+ */
+static inline uint32_t div_u32_mod_10(uint32_t n)
+{
+ return n - (div_u32_by_10(n)*10);
+}
+
+#ifdef __cplusplus
+}
+#endif
+/** @} */
+#endif /* DIV_H */
--
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