bench_frac_div: Benchmark for different scaling methods

tests/bench_frac_div/Makefile

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+include ../Makefile.tests_common
+
+USEMODULE += frac
+USEMODULE += div
+USEMODULE += xtimer
+
+include $(RIOTBASE)/Makefile.include

tests/bench_frac_div/README.md

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+Benchmark division
+==================
+
+This benchmark compares performance of the frac and div modules against the
+compiler generated division code.
+An array of TEST_NUMOF pseudorandom numbers is used as the input to the scaling
+functions.
+The same scale factor is applied using three different methods: traditional
+division operator (z = x / y), the frac module (z = frac_scale(frac, x)), and
+the div module (where applicable, e.g. z = div_u64_by_1000000(x))
+One test uses the constant 512/15625 scaling factor used by
+xtimer_ticks_from_usec when using a 32768 Hz timer. A constant scaling factor
+may receive extra optimization in the compiler, so the benchmark additionally
+provides two more tests of a varying denominator and a varying numerator.
+
+Results
+=======
+
+The output shows the execution time (in usec by default) required for scaling
+TEST_NUMOF number of pseudorandom uin64_t values with a the same scaling factor.

tests/bench_frac_div/main.c

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+/*
+ * Copyright (C) 2018 Eistec AB
+ *
+ * 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.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       Division code benchmark
+ *
+ * @author      Joakim Nohlgård <joakim.nohlgard@eistec.se>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <inttypes.h>
+
+#include "frac.h"
+#include "div.h"
+#include "periph/timer.h"
+
+#ifndef TEST_NUMOF
+#define TEST_NUMOF       4096
+#endif
+
+#ifndef TIM_REF_DEV
+#define TIM_REF_DEV     TIMER_DEV(0)
+#endif
+
+#ifndef TIM_REF_FREQ
+#define TIM_REF_FREQ    1000000ul
+#endif
+
+/* working area */
+static uint64_t buf[TEST_NUMOF];
+
+#define ARRAY_LEN(arr) (sizeof(arr) / sizeof((arr)[0]))
+
+/* Apply div_u64_by_15625div512 on all elements of buf */
+uint32_t bench_div_u64_by_15625div512(uint64_t *buf, size_t nelem)
+{
+    unsigned time_start = timer_read(TIM_REF_DEV);
+    for (unsigned k = 0; k < nelem; ++k) {
+        buf[k] = div_u64_by_15625div512(buf[k]);
+    }
+    unsigned time_end = timer_read(TIM_REF_DEV);
+    return (time_end - time_start);
+}
+
+/* Use frac_scale on all elements of buf */
+uint32_t bench_frac(uint64_t *buf, size_t nelem, uint32_t num, uint32_t den)
+{
+    frac_t frac;
+    frac_init(&frac, num, den);
+    unsigned time_start = timer_read(TIM_REF_DEV);
+    for (unsigned k = 0; k < nelem; ++k) {
+        buf[k] = frac_scale(&frac, buf[k]);
+    }
+    unsigned time_end = timer_read(TIM_REF_DEV);
+    return (time_end - time_start);
+}
+
+/* Use div_u64_by_1000000 to compute a fractional scale on all elements of buf */
+uint32_t bench_div_u64_by_1000000(uint64_t *buf, size_t nelem, uint32_t num)
+{
+    unsigned time_start = timer_read(TIM_REF_DEV);
+    for (unsigned k = 0; k < nelem; ++k) {
+        uint64_t x = buf[k];
+        uint64_t q = div_u64_by_1000000(x);
+        uint32_t r = x - q * num;
+        buf[k] = q + div_u64_by_1000000((uint64_t)r * num);
+    }
+    unsigned time_end = timer_read(TIM_REF_DEV);
+    return (time_end - time_start);
+}
+
+/* Use 64 bit division operator on all elements of buf */
+uint32_t bench_divide(uint64_t *buf, size_t nelem, uint32_t num, uint32_t den)
+{
+    unsigned time_start = timer_read(TIM_REF_DEV);
+    for (unsigned k = 0; k < nelem; ++k) {
+        uint64_t x = buf[k];
+        uint64_t q = x / den;
+        uint32_t r = x - q * num;
+        buf[k] = q + ((uint64_t)r * num) / den;
+    }
+    unsigned time_end = timer_read(TIM_REF_DEV);
+    return (time_end - time_start);
+}
+
+void timer_cb(void *arg, int chan)
+{
+    (void) arg;
+    (void) chan;
+    puts("Warning! spurious timer interrupt");
+}
+
+void fill_buf(uint64_t *buf, size_t nelem, uint64_t seed)
+{
+    for (unsigned k = 0; k < nelem; ++k) {
+        seed = 6364136223846793005ull * seed + 1;
+        buf[k] = seed;
+    }
+}
+
+int main(void)
+{
+    puts("Division benchmark");
+
+    puts("Init timer");
+    printf("TIM_REF_DEV: %u\n", (unsigned)TIM_REF_DEV);
+    printf("TIM_REF_FREQ: %lu\n", (unsigned long)TIM_REF_FREQ);
+    int res = timer_init(TIM_REF_DEV, TIM_REF_FREQ, timer_cb, NULL);
+    if (res < 0) {
+        puts("Error initializing timer!");
+        while(1) {}
+    }
+    uint64_t seed = 12345;
+    uint32_t variation = 4321;
+    while (1) {
+        ++seed;
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        uint32_t time_div = bench_div_u64_by_15625div512(buf, ARRAY_LEN(buf));
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        uint32_t time_frac = bench_frac(buf, ARRAY_LEN(buf), 512, 15625);
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        uint32_t time_divide = bench_divide(buf, ARRAY_LEN(buf), 512, 15625);
+        printf("const (  512 /   15625) /,%%: %8" PRIu32 " frac: %8" PRIu32 " div: %8" PRIu32 "\n", time_divide, time_frac, time_div);
+        uint32_t var = variation % 10000ul + 995000ul;
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        time_div = bench_div_u64_by_1000000(buf, ARRAY_LEN(buf), var);
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        time_frac = bench_frac(buf, ARRAY_LEN(buf), var, 1000000ul);
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        time_divide = bench_divide(buf, ARRAY_LEN(buf), var, 1000000ul);
+        printf("var (%7" PRIu32 " / 1000000) /,%%: %8" PRIu32 " frac: %8" PRIu32 " div: %8" PRIu32 "\n", var, time_divide, time_frac, time_div);
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        time_frac = bench_frac(buf, ARRAY_LEN(buf), 1000000ul, var);
+        fill_buf(buf, ARRAY_LEN(buf), seed);
+        time_divide = bench_divide(buf, ARRAY_LEN(buf), 1000000ul, var);
+        printf("var (1000000 / %7" PRIu32 ") /,%%: %8" PRIu32 " frac: %8" PRIu32 " div: [no implementation]\n", var, time_divide, time_frac);
+        ++variation;
+    }
+    return 0;
+}