Change trashes → clobbers in calculator.asm

calculator.asm

@@ -1,8 +1,6 @@
 org 0
 
 start:
-	cleq r0, r0, initStack
-
 	load r0, lit01
 	load r1, litff
 	cleq r0, r0, pushWord
@@ -37,17 +35,27 @@ stAdd:
 
 ; a b -- a-b
 stSub:
-	cleq r0, r0, stNeg
-	breq r0, r0, stAdd
-
-; n -- -n
-stNeg:
 	cleq r0, r0, popWord
-	nand r0, r0
-	nand r1, r1
-	cleq r0, r0, incWord
+	cleq r0, r0, tmpStoreWord01
+	cleq r0, r0, popWord
+	cleq r0, r0, tmpLoadWord23
+	cleq r0, r0, subWord
 	breq r0, r0, pushWord
 
+; a b --
+; if a >= b then r0:r1 = 0001
+; else r0:r1 = 0000
+stGtEq:
+	cleq r0, r0, popWord
+	cleq r0, r0, tmpStoreWord01
+	cleq r0, r0, popWord
+	cleq r0, r0, tmpLoadWord23
+	cleq r0, r0, subWord
+	xor r0, r0
+	xor r1, r1
+	or r1, r2
+	ret
+
 ; ------------------------------------------------------------------
 ; I/O
 ; ------------------------------------------------------------------
@@ -83,6 +91,8 @@ tmpWordLow: data 0
 
 ; out:
 ;  r0:r1 = word
+; clobbers:
+;  r2, r3
 peekWord:
 	cleq r0, r0, popWord
 	cleq r0, r0, tmpStoreWord01
@@ -112,7 +122,7 @@ tmpLoadWord23:
 
 ; in:
 ;  r0:r1 = word
-; trashes:
+; clobbers:
 ;  r0, r1, r2, r3
 pushWord:
 	store pushWordLow, r1
@@ -124,7 +134,7 @@ pushWord:
 
 ; out:
 ;  r0:r1
-; trashes:
+; clobbers:
 ;  r2, r3
 popWord:
 	cleq r0, r0, popByte
@@ -140,33 +150,33 @@ popWord:
 
 ; in:
 ;  r0 = byte
-; trashes:
+; clobbers:
 ;  r0, r1, r2, r3
 pushByte:
-	load r2, SPHigh
+	load r2, SP+0
 	store storeByteHigh, r2
-	load r3, SPLow
+	load r3, SP+1
 	store storeByteLow, r3
 	cleq r0, r0, storeByte
 
-	load r0, SPHigh
-	load r1, SPLow
+	load r0, SP+0
+	load r1, SP+1
 	cleq r0, r0, incWord
-	store SPHigh, r0
-	store SPLow, r1
+	store SP+0, r0
+	store SP+1, r1
 
 	ret
 
 ; out:
 ;  r0 = byte
-; trashes:
+; clobbers:
 ;  r1, r2, r3
 popByte:
-	load r0, SPHigh
-	load r1, SPLow
+	load r0, SP+0
+	load r1, SP+1
 	cleq r0, r0, decWord
-	store SPHigh, r0
-	store SPLow, r1
+	store SP+0, r0
+	store SP+1, r1
 
 	store loadByteHigh, r0
 	store loadByteLow, r1
@@ -201,7 +211,7 @@ loadByte:
 ; out:
 ;  r0:r1 = result
 ;  r2 = carryout
-; trashes:
+; clobbers:
 ;  r3
 addWord:
 	store addWordFirstHigh, r0
@@ -230,9 +240,48 @@ addWord:
 	addWordSecondHigh: data 0
 	addWordResultLow: data 0
 
+; in:
+;  r0:r1 = minuend
+;  r2:r3 = subtrahend
+; out:
+;  r0:r1 = result
+;  r2 = carryout
+; clobbers:
+;  r3
+subWord:
+	store subWordMinuendHigh, r0
+	store subWordSubtrahendHigh, r2
+
+	; Subtract low bytes
+	; a - b = a + (-b) = a + ~b + 1
+	xor r0, r0
+	or r0, r3
+	nand r0, r0
+	load r2, lit01
+	cleq r0, r0, addByte3
+	store subWordResultLow, r0
+
+	; Subtract high bytes with carry-in in r1
+	load r0, subWordMinuendHigh
+	load r2, subWordSubtrahendHigh
+	nand r2, r2
+	cleq r0, r0, addByte3
+
+	; Move carryout to r2
+	xor r2, r2
+	or r2, r1
+
+	load r1, subWordResultLow
+
+	ret
+
+	subWordMinuendHigh: data 0
+	subWordSubtrahendHigh: data 0
+	subWordResultLow: data 0
+
 ; in/out:
 ;  r0:r1 = word
-; trashes:
+; clobbers:
 ;  r2, r3
 incWord:
 	store incWordHigh, r0
@@ -255,7 +304,7 @@ incWord:
 
 ; in/out:
 ;  r0:r1 = word
-; trashes:
+; clobbers:
 ;  r2, r3
 decWord:
 	store decWordHigh, r0
@@ -284,7 +333,7 @@ decWord:
 ; out:
 ;  r0 = result
 ;  r1 = carryout
-; trashes:
+; clobbers:
 ;  r2, r3
 addByte3:
 	store addByte3ThirdAddend, r2
@@ -309,7 +358,7 @@ addByte3:
 ; out:
 ;  r0 = result
 ;  r1 = carryout
-; trashes:
+; clobbers:
 ;  r2, r3
 addByte:
 	; Initiliaze carryout to 0
@@ -356,7 +405,7 @@ addByte:
 ;  r0 = number in range [0, 0xf]
 ; out:
 ;  r0 = ascii character corresponding to input
-; trashes:
+; clobbers:
 ;  r3
 nybble2hex:
 	xor r3, r3
@@ -447,7 +496,7 @@ nybble2hex:
 ;  r0 = ascii hex digit
 ; out:
 ;  r0 = corresponding nybble
-; trashes:
+; clobbers:
 ;  r3
 hex2nybble:
 	load r3, litchar0
@@ -552,7 +601,7 @@ hex2nybble:
 
 ; in:
 ;  r1:r0 = word
-; trashes:
+; clobbers:
 ;  r0, r2, r3
 writehexWord:
 	cleq r0, r0, writehexByte
@@ -564,7 +613,7 @@ writehexWord:
 
 ; in:
 ;  r0 = byte
-; trashes:
+; clobbers:
 ;  r0, r2, r3
 writehexByte:
 	; Store copy of the byte (as r0 is modified by nybble2hex)
@@ -591,7 +640,7 @@ writehexByte:
 ; Common output routines
 ; ------------------------------------------------------------------
 
-; trashes:
+; clobbers:
 ;  r3
 newline:
 	load r3, litcharCR
@@ -695,18 +744,5 @@ litff: data ff
 ; Stack
 ; ==================================================================
 
-SPHigh: data 0
-SPLow: data 0
-
-; trashes:
-;  r3
-initStack:
-	load r3, initStackDummyLoad+1
-	store SPHigh, r3
-	load r3, initStackDummyLoad+2
-	store SPLow, r3
-	ret
-
-	initStackDummyLoad: load r0, stackBase
-
+SP: addr stackBase
 stackBase: