Differences

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--- base:16-bit_comparison [2020-10-22 20:30] – created tww
+++ base:16-bit_comparison [2020-10-27 00:34] – tww_ctr
@@ Line 4: / Line 4: @@
-TWW method:
+bit equivalent of the CMP OPC:
 <code>
 /*! «»«»«»«»{CMP16}«»«»«»«»
-    Does exactly the same as CMP of two values (effectively its a val1-val2) and sets the flags as follows:
+    Does exactly the same as CMP of two values (effectively its a A - M) and sets the flags as follows:
-                       (BCC/BCS)      (BEQ/BNE)      (BMI/BPL)
+    If A = M : Carry =  SET   Zero =  SET   Negative = CLEAR
-    If val1 = val2 : Carry =  SET   Zero =  SET   Negative = CLEAR
+    If A > M : Carry =  SET   Zero = CLEAR  Negative = CLEAR
-    If val1 > val2 : Carry =  SET   Zero = CLEAR  Negative = CLEAR
+    If A < M : Carry = CLEAR  Zero = CLEAR  Negative =  SET
-    If val1 < val2 : Carry = CLEAR  Zero = CLEAR  Negative =  SET
 */
-    lda val1
+    lda A+1
-    sec
+    cmp M+1
-    sbc val2
+    bne !+
-    php
+        lda A
-    lda val1+1
+        cmp M
-    sbc val2+1
+!:
-    php
+    // Status register sorted, from here you can branch as you like as you would after a CMP opc.
-    pla
+</code>
-    sta temp
-    pla
-    and #%00000010
-    ora #%11111101
-    and temp
-    pha
-    plp
-Somewhere on ZP:
-temp:
-    .byte $00
+Different approach: instead of setting flags, goes to different destinations:
+<code>
+; Val1 ≥ Val2 ?
+  LDA Val1 +1    ; high bytes
+  CMP Val2+1
+  BCC LsThan     ; hiVal1 < hiVal2 --> Val1 < Val2
+  BNE GrtEqu     ; hiVal1 ≠ hiVal2 --> Val1 > Val2
+  LDA Val1       ; low bytes
+  CMP Val2
+  ;BEQ Equal     ; Val1 = Val2
+  BCS GrtEqu     ; loVal1 ≥ loVal2 --> Val1 ≥ Val2
+LsThan
+...
+GrtEqu
+...
 </code>