moved multiplication function to "common" dir, added divide routine.

avr/common/multiply.asm

@@ -0,0 +1,69 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+#ifndef COMMON_MULTIPLY_H
+#define COMMON_MULTIPLY_H
+
+
+; ---------------------------------------------------------------------------
+; @routine Utils_Mulu16x16_32
+;
+; Multiplies two unsigned 16 bit values resulting in one 32 bit value.
+; This is a rather simple but reasonable fast routine working just like you would
+; when doing multiplications with pen and paper.
+;
+; R19:R18:R17:R16 = R21:R20 * R23:R22
+;
+; TODO: adapt for signed values
+;
+; @param  R21:R20 16 bit value A
+; @param  R23:R22 16 bit value B
+; @return R19:R18:R17:R16 32 bit result
+; @clobbers R16, R17, R18, R19, R20, R21, R22, R23, R24, R25, R26
+
+Utils_Mulu16x16_32:
+  clr r19
+  clr r18
+  clr r17
+  clr r16
+  clr r25
+  clr r24
+  ldi r26, 16                     ; 16 bit multiplicator
+Utils_Mulu16x16_32_loop:
+    lsr r23
+    ror r22
+    brcc Utils_Mulu16x16_32_noadd ; current digit in B is 0, don't add shifted A to result
+    add r16, r22
+    adc r17, r23
+    adc r18, r24
+    adc r19, r25
+;    brcs Utils_Mulu16x16_32_overflow ; can't happen
+Utils_Mulu16x16_32_noadd:
+    dec r26
+    breq Utils_Mulu16x16_32_done
+    lsl r20
+    rol r21
+    rol r24
+    rol r25
+;    brcs Utils_Mulu16x16_32_overflow ; can't happen
+  rjmp Utils_Mulu16x16_32_loop
+Utils_Mulu16x16_32_done:
+  clc
+  ret
+;Utils_Mulu16x16_32_overflow:  ; never reached. Multiplying 2 16 bit values can't overflow 32 bit
+;  sec
+;  ret
+; @end
+
+
+
+
+
+#endif ; COMMON_MULTIPLY_H
+