Switch trigonometric implementation, saves 460b memory

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ### Builds after release 0.12.0
 
+#### Build 2104141
+
+-   Reduced memory usage by 540b by switching to a different trigonometric approximation
+
 #### Build 2104140
 
 -   Added dynamic location-based Sunrise/Sunset macros (PR #1889)

wled00/ntp.cpp

@@ -1,5 +1,6 @@
 #include "src/dependencies/timezone/Timezone.h"
 #include "wled.h"
+#include "wled_math.h"
 
 /*
  * Acquires time from NTP server
@@ -316,8 +317,8 @@ void checkTimers()
 // get sunrise (or sunset) time (in minutes) for a given day at a given geo location
 int getSunriseUTC(int year, int month, int day, float lat, float lon, bool sunset=false) {
   //1. first calculate the day of the year
-  float N1 = floor(275 * month / 9);
-  float N2 = floor((month + 9) / 12);
+  float N1 = 275 * month / 9;
+  float N2 = (month + 9) / 12;
   float N3 = (1 + floor((year - 4 * floor(year / 4) + 2) / 3));
   float N = N1 - (N2 * N3) + day - 30;
 
@@ -329,10 +330,10 @@ int getSunriseUTC(int year, int month, int day, float lat, float lon, bool sunse
   float M = (0.9856 * t) - 3.289;
 
   //4. calculate the Sun's true longitude
-  float L = fmod(M + (1.916 * sin(DEG_TO_RAD*M)) + (0.020 * sin(2*DEG_TO_RAD*M)) + 282.634, 360.0);
+  float L = fmod(M + (1.916 * sin_t(DEG_TO_RAD*M)) + (0.020 * sin_t(2*DEG_TO_RAD*M)) + 282.634, 360.0);
 
   //5a. calculate the Sun's right ascension      
-  float RA = fmod(RAD_TO_DEG*atan(0.91764 * tan(DEG_TO_RAD*L)), 360.0);
+  float RA = fmod(RAD_TO_DEG*atan_t(0.91764 * tan_t(DEG_TO_RAD*L)), 360.0);
 
   //5b. right ascension value needs to be in the same quadrant as L   
   float Lquadrant  = floor( L/90) * 90;
@@ -343,16 +344,16 @@ int getSunriseUTC(int year, int month, int day, float lat, float lon, bool sunse
   RA /= 15.;
 
   //6. calculate the Sun's declination
-  float sinDec = 0.39782 * sin(DEG_TO_RAD*L);
-  float cosDec = cos(asin(sinDec));
+  float sinDec = 0.39782 * sin_t(DEG_TO_RAD*L);
+  float cosDec = cos_t(asin_t(sinDec));
 
   //7a. calculate the Sun's local hour angle
-  float cosH = (sin(DEG_TO_RAD*ZENITH) - (sinDec * sin(DEG_TO_RAD*lat))) / (cosDec * cos(DEG_TO_RAD*lat));
+  float cosH = (sin_t(DEG_TO_RAD*ZENITH) - (sinDec * sin_t(DEG_TO_RAD*lat))) / (cosDec * cos_t(DEG_TO_RAD*lat));
   if (cosH > 1 && !sunset) return 0;  // the sun never rises on this location (on the specified date)
   if (cosH < -1 && sunset) return 0;  // the sun never sets on this location (on the specified date)
 
   //7b. finish calculating H and convert into hours
-  float H = sunset ? RAD_TO_DEG*acos(cosH) : 360 - RAD_TO_DEG*acos(cosH);
+  float H = sunset ? RAD_TO_DEG*acos_t(cosH) : 360 - RAD_TO_DEG*acos_t(cosH);
   H /= 15.;
 
   //8. calculate local mean time of rising/setting      

wled00/wled.h

@@ -8,7 +8,7 @@
  */
 
 // version code in format yymmddb (b = daily build)
-#define VERSION 2104140
+#define VERSION 2104141
 
 //uncomment this if you have a "my_config.h" file you'd like to use
 //#define WLED_USE_MY_CONFIG

wled00/wled_math.h

@@ -0,0 +1,71 @@
+#ifndef WLED_MATH_H
+#define WLED_MATH_H
+
+/*
+ * Contains some trigonometric functions.
+ * The ANSI C equivalents are likely faster, but using any sin/cos/tan function incurs a memory penalty of 460 bytes on ESP8266, likely for lookup tables.
+ * This implementation has no extra static memory usage.
+ * 
+ * Source of the cos_t() function: https://web.eecs.utk.edu/~azh/blog/cosine.html (cos_taylor_literal_6terms)
+ */
+
+#include <Arduino.h> //PI constant
+
+#define modd(x, y) ((x) - (int)((x) / (y)) * (y))
+
+double cos_t(double x)
+{
+  x = modd(x, TWO_PI);
+  char sign = 1;
+  if (x > PI)
+  {
+      x -= PI;
+      sign = -1;
+  }
+  double xx = x * x;
+
+  return sign * (1 - ((xx) / (2)) + ((xx * xx) / (24)) - ((xx * xx * xx) / (720)) + ((xx * xx * xx * xx) / (40320)) - ((xx * xx * xx * xx * xx) / (3628800)) + ((xx * xx * xx * xx * xx * xx) / (479001600)));
+}
+
+double sin_t(double x) {
+  return cos_t(HALF_PI - x);
+}
+
+double tan_t(double x) {
+  double c = cos_t(x);
+  if (c==0.0) return 0;
+  return sin_t(x) / c;
+}
+
+//https://stackoverflow.com/questions/3380628
+// Absolute error <= 6.7e-5
+float acos_t(float x) {
+  float negate = float(x < 0);
+  x = std::abs(x);
+  float ret = -0.0187293;
+  ret = ret * x;
+  ret = ret + 0.0742610;
+  ret = ret * x;
+  ret = ret - 0.2121144;
+  ret = ret * x;
+  ret = ret + HALF_PI;
+  ret = ret * sqrt(1.0-x);
+  ret = ret - 2 * negate * ret;
+  return negate * PI + ret;
+}
+
+float asin_t(float x) {
+  return HALF_PI - acos_t(x);
+}
+
+//https://stackoverflow.com/a/42542593
+#define A 0.0776509570923569
+#define B -0.287434475393028
+#define C ((HALF_PI/2) - A - B)
+
+double atan_t(double x) {
+  double xx = x * x;
+  return ((A*xx + B)*xx + C)*x;
+}
+
+#endif