Code review adaptations, removed "cc65_" prefix from functions

[cc65] / libsrc / common / mul40.s

diff --git a/libsrc/common/mul40.s b/libsrc/common/mul40.s
new file mode 100644 (file)
index 0000000..f240fc4
--- /dev/null
+++ b/libsrc/common/mul40.s
@@ -0,0 +1,50 @@
+; mul40.s
+;
+; This file is part of
+; cc65 - a freeware C compiler for 6502 based systems
+;
+; https://github.com/cc65/cc65
+;
+; See "LICENSE" file for legal information.
+;
+;
+; unsigned int __fastcall__ mul40(unsigned char value);
+; 
+; REMARKS: Function is defined to return with carry-flag cleared
+
+
+        .importzp       tmp4
+        .export         _mul40
+
+.proc   _mul40                  ; = 33 bytes, 48/53 cycles
+
+        sta     tmp4            ; remember value for later addition...
+        ldx     #0              ; clear high-byte
+        asl     a               ; * 2
+        bcc     mul4            ; high-byte affected?
+        ldx     #2              ; this will be the 1st high-bit soon...
+
+mul4:   asl     a               ; * 4
+        bcc     mul5            ; high-byte affected?
+        inx                     ; => yes, apply to 0 high-bit
+        clc                     ; prepare addition
+
+mul5:   adc     tmp4            ; * 5
+        bcc     mul10           ; high-byte affected?
+        inx                     ; yes, correct...
+
+mul10:  stx     tmp4            ; continue with classic shifting...
+        
+        asl     a               ; * 10
+        rol     tmp4
+
+        asl     a               ; * 20
+        rol     tmp4
+
+        asl     a               ; * 40
+        rol     tmp4
+
+        ldx     tmp4            ; deliver high-byte in X
+        rts
+
+.endproc