From 5119c38ca6d2370fda8fc7b03147f97b8bbb5f53 Mon Sep 17 00:00:00 2001
From: Martin Preuss <martin@aquamaniac.de>
Date: Sun, 15 Mar 2026 20:20:33 +0100
Subject: [PATCH] avr: added divide8

---
 avr/common/divide.asm  |  5 ++++
 avr/common/divide8.asm | 60 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 avr/common/divide8.asm

diff --git a/avr/common/divide.asm b/avr/common/divide.asm
index 0609b02..bf125ab 100644
--- a/avr/common/divide.asm
+++ b/avr/common/divide.asm
@@ -57,3 +57,8 @@ Utils_Divu16_16_16_loop_end:
 ; @end
 
 
+
+#endif
+
+
+
diff --git a/avr/common/divide8.asm b/avr/common/divide8.asm
new file mode 100644
index 0000000..ff46e65
--- /dev/null
+++ b/avr/common/divide8.asm
@@ -0,0 +1,60 @@
+; ***************************************************************************
+; 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_DIVIDE8_H
+#define COMMON_DIVIDE8_H
+
+
+
+
+
+; ---------------------------------------------------------------------------
+; @routine Utils_Divu8_8_8
+;
+; Divides two unsigned 8 bit values resulting in one 8 bit value.
+; This is a rather simple but reasonable fast routine working just like you would
+; when doing divisions with pen and paper.
+;
+; R16 = R18  /  R19
+; R17 = R18 mod R19
+
+; TODO: adapt for signed values
+;
+; @param  R18 8 bit value A
+; @param  R19 8 bit value B
+; @return R16 8 bit result
+; @return R17 8 bit remainder
+; @clobbers R25
+
+
+Utils_Divu8_8_8:
+  mov r16, r18                    ; r16=result (intitially: dividend)
+  clr r17                         ; r17=remainder
+  ldi r25, 8                      ; 8 bits to divide
+Utils_Divu8_8_8_loop:
+    lsl r16                       ; shift 0 bit into result
+    rol r17
+    
+    sub r17, r19                  ; try to subtract divisor from value
+    brcs Utils_Divu8_8_8_nofit    ; jmp if dividend < divisor
+    ori r16, 1                    ; otherwise set bit in result
+    rjmp Utils_Divu8_8_8_loop_end
+Utils_Divu8_8_8_nofit:
+    add r17, r19                  ; undo subtraction
+    ; r16=result
+Utils_Divu8_8_8_loop_end:
+    dec r25
+  brne Utils_Divu8_8_8_loop
+  ret
+; @end
+
+
+
+#endif
+