fixedmath: add square root and b32_t conversion operators

2026-06-06 08:36:24 +08:00 · 2017-05-04 06:50:08 -06:00
parent aa1509bacb
commit afc46cb7ba
3 changed files with 173 additions and 7 deletions
@@ -36,6 +36,7 @@
 # Add the fixed precision math C files to the build

 CSRCS += lib_fixedmath.c lib_b16sin.c lib_b16cos.c lib_b16atan2.c
+CSRCS += lib_ubsqrt.c

 # Add the fixed precision math directory to the build

@@ -0,0 +1,136 @@
+/****************************************************************************
+ * libc/fixedmath/lib_ubsqrt.c
+ *
+ *   Copyright (C) 2014,2017 Jussi Kivilinna <jussi.kivilinna@haltian.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <fixedmath.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+#ifdef CONFIG_HAVE_LONG_LONG
+
+/****************************************************************************
+ * Name: ub32sqrtub16
+ *
+ * Description:
+ *   ub32sqrtub16 calculates square root for 'a'
+ *
+ ****************************************************************************/
+
+ub16_t ub32sqrtub16(ub32_t a)
+{
+  uint64_t n = a;
+  uint64_t xk = n;
+
+  /* Direct conversion of ub32_t to uint64_t is same operation as multiplying
+   * 'a' by 2^32, therefore n = a * 2^32.
+   */
+
+  if (xk == UINT64_MAX)
+    {
+      /* Avoid 'xk + n / xk' overflow on first iteration. */
+
+      xk = 1ULL << 63;
+    }
+
+  do
+    {
+      uint64_t xk1 = (xk + n / xk) >> 1;
+
+      if (xk1 >= xk)
+        {
+          break;
+        }
+
+      xk = xk1;
+    }
+  while (1);
+
+  /* 'xk' now holds 'sqrt(n)' => 'sqrt(a * 2^32)' => 'sqrt(a) * 2^16', thus
+   * 'xk' holds square root of 'a' in ub16_t format.
+   */
+
+  return (ub16_t)xk;
+}
+
+#endif
+
+/****************************************************************************
+ * Name: ub16sqrtub8
+ *
+ * Description:
+ *   ub16sqrtub8 calculates square root for 'a'
+ *
+ ****************************************************************************/
+
+ub8_t ub16sqrtub8(ub16_t a)
+{
+  uint32_t n = a;
+  uint32_t xk = n;
+
+  /* Direct conversion of ub16_t to uint32_t is same operation as multiplying
+   * 'a' by 2^16, therefore n = a * 2^16.
+   */
+
+  if (xk == UINT32_MAX)
+    {
+      /* Avoid 'xk + n / xk' overflow on first iteration. */
+
+      xk = 1U << 31;
+    }
+
+  do
+    {
+      uint32_t xk1 = (xk + n / xk) >> 1;
+
+      if (xk1 >= xk)
+        {
+          break;
+        }
+
+      xk = xk1;
+    }
+  while (1);
+
+  /* 'xk' now holds 'sqrt(n)' => 'sqrt(a * 2^16)' => 'sqrt(a) * 2^8', thus
+   * 'xk' holds square root of 'a' in ub8_t format.
+   */
+
+  return (ub8_t)xk;
+}