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--- base:multiplication_with_a_constant [2020-04-09 21:30] – Added credits ftc
+++ base:multiplication_with_a_constant [2021-02-10 01:24] (current) – fix a typo strobe
@@ Line 1: / Line 1: @@
 ====== Multiplication with a constant ======
-By TWW
 Multiplication by a specific constant can be a lot simpler and faster than a general-purpose routine to multiply two given numbers together.
@@ Line 20: / Line 18: @@
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-EDIT: The above is based on 8*A + 2*A. This routine would not allow any higher number than A = 25 as it would overflow (8 * 26) + (2 * 26) = 208 + 52 = 262 (However 25 fits perfectly f.ex. when you'd want to calculate a character line based on Y).
+By TWW:
+Optimization of the above posted by unknown: The above is based on 8*A + 2*A. This routine would not allow any higher number than A = 25 as it would overflow (8 * 26) + (2 * 26) = 208 + 52 = 262 (However 25 fits perfectly f.ex. when you'd want to calculate a character line based on Y).
 With this in mind, you can do 2*A + 8*A which saves you the asl $2. Also as long as A cannot be higher than 25, the upper 4 bits (high nybble) will always be #%0000. This means that the asl instructions will never set carry and the clc can be dropped.
-This gives the following code to multiply A with 10 (assuming A is less than 25):
+This gives the following code to multiply A with 10 (assuming A is less than 26):
 <code>