Convert rand multiplication constants to shifts and adds.

Since many popular low-cost chipsets do not have a native multiply operation,
this calculation can be executed much more efficiently using only add and left shift.

1 files changed, 5 insertions, 2 deletions

diff --git a/lib8tion/random8.h b/lib8tion/random8.h
index ba60cf57..ab9ac27e 100644
--- a/lib8tion/random8.h
+++ b/lib8tion/random8.h
@@ -12,13 +12,16 @@
 #define FASTLED_RAND16_2053  ((uint16_t)(2053))
 #define FASTLED_RAND16_13849 ((uint16_t)(13849))
 
+// equivalent to x * 2053
+#define APPLY_FASTLED_RAND16_2053(x) (x << 11) + (x << 2) + x
+
 /// random number seed
 extern uint16_t rand16seed;// = RAND16_SEED;
 
 /// Generate an 8-bit random number
 LIB8STATIC uint8_t random8()
 {
-    rand16seed = (rand16seed * FASTLED_RAND16_2053) + FASTLED_RAND16_13849;
+    rand16seed = APPLY_FASTLED_RAND16_2053(rand16seed) + FASTLED_RAND16_13849;
     // return the sum of the high and low bytes, for better
     //  mixing and non-sequential correlation
     return (uint8_t)(((uint8_t)(rand16seed & 0xFF)) +
@@ -28,7 +31,7 @@ LIB8STATIC uint8_t random8()
 /// Generate a 16 bit random number
 LIB8STATIC uint16_t random16()
 {
-    rand16seed = (rand16seed * FASTLED_RAND16_2053) + FASTLED_RAND16_13849;
+    rand16seed = APPLY_FASTLED_RAND16_2053(rand16seed) + FASTLED_RAND16_13849;
     return rand16seed;
 }