Merge #19378

19378: sys: add common imath module mv isin() form test/driver_dac_dds r=maribu a=benpicco



Co-authored-by: Benjamin Valentin <[email protected]>

sys/include/imath.h

@@ -0,0 +1,144 @@
+/*
+ * Copyright (C) 2023 ML!PA Consulting GmbH
+ *
+ * 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.
+ */
+
+/**
+ * @defgroup    sys_imath   imath: Integer Math functions
+ * @ingroup     sys
+ *
+ * @brief       This modules provides some integer-only math functions.
+ *              They can be used when no FPU is available or no exact
+ *              precision is needed.
+ *
+ * @author      Karl Fessel <[email protected]>
+ * @{
+ */
+
+#ifndef IMATH_H
+#define IMATH_H
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define SINI_PERIOD      0x8000 /**< Period of the fast_sini() function */
+#define SINI_MAX         0x1000 /**< Max value of the fast_sini() function */
+#define SINI_MIN        -0x1000 /**< Min value of the fast_sini() function */
+
+/**
+ * @brief       Internal fast_sini/fast_cosi helper function
+ * @internal
+ *
+ * @param[in] x Input parameter
+ *
+ * @return      absolute value of cosine
+ */
+static inline  __attribute__((always_inline))
+int32_t _ihelp(int32_t x)
+{
+    int32_t y;
+    static const int32_t qN = 13,
+                         qA = 12,
+                          B = 19900,
+                          C = 3516;
+
+    x = x << (31 - qN);         /* Mask with PI                 */
+    x = x >> (31 - qN);         /* Note: SIGNED shift! (to qN)  */
+    x = x * x >> (2 * qN - 14); /* x=x^2 To Q14                 */
+
+    y = B - (x * C >> 14);      /* B - x^2*C                    */
+    y = (1 << qA)               /* A - x^2*(B-x^2*C)            */
+      - (x * y >> 16);
+
+    return y;
+}
+
+/**
+ * @brief A sine approximation via a fourth-order cosine approx.
+ *        source: https://www.coranac.com/2009/07/sines/
+ *
+ * @param x     angle (with 2^15 units/circle)
+ * @return      sine value (-2^12 ≤ y ≤ 2^12)
+ */
+static inline int32_t fast_sini(int32_t x)
+{
+    static const int32_t qN = 13;
+
+    int32_t c = x << (30 - qN);
+    int32_t y = _ihelp(x - (1 << qN));
+
+    return c >= 0 ? y :-y;
+}
+
+/**
+ * @brief A a fourth-order cosine approx.
+ *        source: https://www.coranac.com/2009/07/sines/
+ *
+ * @param x     angle (with 2^15 units/circle)
+ * @return      sine value (-2^12 ≤ y ≤ 2^12)
+ */
+static inline int32_t fast_cosi(int32_t x)
+{
+    static const int32_t qN = 13;
+
+    int32_t c = (x + (SINI_PERIOD >> 2)) << (30 - qN);
+    int32_t y = _ihelp(x);
+
+    return c >= 0 ? y :-y;
+}
+
+/**
+ * @brief Square root of an integer
+ *
+ * @param x unsigned integer value
+ * @return  square root of @p x
+ */
+static inline unsigned sqrti(unsigned x)
+{
+    if (x <= 1) {
+        return x;
+    }
+
+    /* initial estimate */
+    unsigned y0 = x >> 1;
+    unsigned y1 = (y0 + x / y0) >> 1;
+
+    while (y1 < y0) {
+        y0 = y1;
+        y1 = (y0 + x / y0) >> 1;
+    }
+
+    return y0;
+}
+
+/**
+ * @brief Returns the value of x to the power of y
+ *
+ * @param x base
+ * @param y exponent
+ *
+ * @return x^y
+ */
+static inline uint32_t powi(unsigned x, unsigned y)
+{
+    uint32_t res = 1;
+
+    while (y--) {
+        res *= x;
+    }
+
+    return res;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* IMATH_H */
+/** @} */

tests/drivers/dac_dds/main.c

@@ -31,6 +31,7 @@
 #include "mutex.h"
 #include "dac_dds.h"
 #include "dac_dds_params.h"
+#include "imath.h"
 #include "shell.h"
 
 #include "blob/hello.raw.h"
@@ -58,38 +59,6 @@
 static bool res_16b = 0;
 static unsigned sample_rate = 8000;
 
-#define ISIN_PERIOD     (0x7FFF)
-#define ISIN_MAX        (0x1000)
-
-/**
- * @brief A sine approximation via a fourth-order cosine approx.
- *        source: https://www.coranac.com/2009/07/sines/
- *
- * @param x     angle (with 2^15 units/circle)
- * @return      sine value (Q12)
- */
-static int32_t isin(int32_t x)
-{
-    int32_t c, y;
-    static const int32_t qN = 13,
-                         qA = 12,
-                          B = 19900,
-                          C = 3516;
-
-    c = x << (30 - qN);         /* Semi-circle info into carry. */
-    x -= 1 << qN;               /* sine -> cosine calc          */
-
-    x = x << (31 - qN);         /* Mask with PI                 */
-    x = x >> (31 - qN);         /* Note: SIGNED shift! (to qN)  */
-    x = x * x >> (2 * qN - 14); /* x=x^2 To Q14                 */
-
-    y = B - (x * C >> 14);      /* B - x^2*C                    */
-    y = (1 << qA)               /* A - x^2*(B-x^2*C)            */
-      - (x * y >> 16);
-
-    return c >= 0 ? y : -y;
-}
-
 /* simple function to fill buffer with samples
  *
  * It is up to the caller to ensure that len is always at least period.
@@ -115,11 +84,11 @@ static void _fill_saw_samples_16(uint8_t *buf, size_t len, uint16_t period)
 static void _fill_sine_samples_8(uint8_t *buf, size_t len, uint16_t period)
 {
     uint16_t x = 0;
-    unsigned step = ISIN_PERIOD / period;
+    unsigned step = SINI_PERIOD / period;
 
     for (uint16_t i = 0; i < period; ++i) {
         x += step;
-        buf[i] = (isin(x) + 4096) >> 6;
+        buf[i] = (fast_sini(x) - SINI_MIN) >> 6;
     }
 
     for (uint16_t i = period; i < len; i += period) {
@@ -130,14 +99,14 @@ static void _fill_sine_samples_8(uint8_t *buf, size_t len, uint16_t period)
 static void _fill_sine_samples_16(uint8_t *buf, size_t len, uint16_t period)
 {
     uint16_t x = 0;
-    unsigned step = ISIN_PERIOD / period;
+    unsigned step = SINI_PERIOD / period;
 
     period *= 2;
 
     for (uint16_t i = 0; i < period; ++i) {
         x += step;
 
-        uint16_t y = (isin(x) + 4096) << 2;
+        uint16_t y = (fast_sini(x) - SINI_MIN) << 2;
         buf[i]   = y;
         buf[++i] = y >> 8;
     }