New code for the shift functions

git-svn-id: svn://svn.cc65.org/cc65/trunk@3143 b7a2c559-68d2-44c3-8de9-860c34a00d81
2004-07-05 22:24:06 +00:00
parent 07419b62f8
commit c122f18605
7 changed files with 240 additions and 406 deletions
--- a/libsrc/runtime/lasr.s
+++ b/libsrc/runtime/lasr.s
@@ -0,0 +1,44 @@
+;
+; Ullrich von Bassewitz, 2004-06-30
+;
+; CC65 runtime: right shift support for longs
+;
+; Note: The standard declares a shift count that is negative or >= the
+; bitcount of the shifted type for undefined behaviour.
+;
+; Note^2: The compiler knowns about the register/zero page usage of this
+; function, so you need to change the compiler source if you change it!
+;
+
+
+       	.export	       	tosasreax
+    	.import	       	popeax
+	.importzp      	sreg, tmp1
+
+
+tosasreax:
+        and     #$1F            ; Bring the shift count into a valid range
+        sta     tmp1            ; Save it
+
+        jsr     popeax          ; Get the left hand operand
+
+        ldy     tmp1            ; Get shift count
+        beq     L9              ; Bail out if shift count zero
+        stx     tmp1            ; Save byte 1
+        ldx     sreg+1          ; Load byte 3
+
+; Do the actual shift. Faster solutions are possible but need a lot more code.
+
+L2:     cpx     #$80            ; Copy bit 31 into the carry
+        ror     sreg+1
+        ror     sreg
+        ror     tmp1
+        ror     a
+        dey
+       	bne    	L2
+
+; Shift done
+
+        ldx     tmp1
+L9:     rts
+