Change the adder to a calculator capable of both adding and subtracting and move error messages to their own lines in it
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@ -1,4 +1,4 @@
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;Two-digit hexadecimal adder
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;Hexadecimal adder and subtractor for two-digit unsigned values
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;Print a prompt
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start: load r0, prompt
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@ -13,9 +13,16 @@ start: load r0, prompt
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;Print a newline
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cleq r0, r0, newln
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;Print a plus sign
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load r0, plus
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store ffff, r0
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;Read the operation sign
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load r0, ffff
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load r1, plus
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breq r0, r1, storsg
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load r1, minus
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breq r0, r1, storsg
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;Error and halt if the character is not a sign
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breq r0, r0, error
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storsg: store sign, r0
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;Print a space
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load r0, space
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store ffff, r0
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@ -34,19 +41,55 @@ start: load r0, prompt
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load r3, equals
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store ffff, r3
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;Add the arguments and load the result to r3
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;Check the operation
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load r3, sign
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load r1, minus
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breq r1, r3, brsub
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;Add and load the result to r3
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;Addition
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cleq r0, r0, adder
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;Load the result to r3
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xor r3, r3
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xor r3, r0
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;Skip the subtraction code
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breq r0, r0, nosign
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;Subtract and load the result to r3
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;Subtraction
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brsub: cleq r0, r0, sub
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;Load the result to r3
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xor r3, r3
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xor r3, r0
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;Convert and print the result
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;Overflow
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;Print a minus sign and unnegate the result if negative
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;Check the sign
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xor r0, r0
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breq r0, r1, nosign
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;Print a minus sign
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load r0, minus
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store ffff, r0
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;Un-negate the result
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store arg1, r3
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load r2, one
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cleq r0, r0, sub
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nand r0, r0
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;Reload the result to r3
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xor r3, r3
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xor r3, r0
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;Skip printing the first digit
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breq r0, r0, skip
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;Print the overflow for addition or zero for positive results of
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;subtraction
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nosign: xor r0, r0
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xor r0, r1
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cleq r0, r0, n2hex
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store ffff, r0
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;Convert and print the result
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;Restore the result back to r0
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xor r0, r0
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skip: xor r0, r0
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xor r0, r3
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;High nibble
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shr r0
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@ -68,6 +111,13 @@ start: load r0, prompt
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;Loop
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breq r0, r0, start
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;Error
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error: cleq r0, r0, newln
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load r0, qmark
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store ffff, r0
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cleq r0, r0, newln
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halt
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;Read and convert an argument and load it to r0
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;First digit
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rarg: load r0, ffff
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@ -89,10 +139,7 @@ rarg2: load r0, ffff
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breq r3, r1, rarg2
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load r1, cr
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breq r3, r1, rarg3
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load r0, qmark
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store ffff, r0
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cleq r0, r0, newln
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halt
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breq r0, r0, error
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;Combine the digits
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rarg3: or r0, r2
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;Return
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@ -151,11 +198,8 @@ hex2n: load r1, tbl01
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breq r0, r1, vale
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load r1, tbl2b
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breq r0, r1, valf
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;Print a question mark and halt if the character is not a digit
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load r0, qmark
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store ffff, r0
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cleq r0, r0, newln
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halt
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;Error and halt if the character is not a digit
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breq r0, r0, error
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;Load the value of the hexadecimal digit
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val0: load r0, tbl00
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breq r0, r0, h2nend
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@ -219,6 +263,25 @@ nvrflw: breq r2, r3, addend
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addend: load r1, ovrflw
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ret
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;Subtract r2 from arg1 and store the result in r0 with the sign
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;bit stored in r1
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;Negate the second argument
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sub: load r0, one
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nand r2, r2
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cleq r0, r0, adder
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;Load the first argument to r2
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load r2, arg1
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;Subtract
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cleq r0, r0, adder
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;Invert the sign bit
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xor r3, r3
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breq r3, r1, submin
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xor r1, r1
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breq r0, r0, subend
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submin: load r1, one
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;Return
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subend: ret
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;Get the hexadecimal digit of a nibble
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;Extract the low nibble
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n2hex: load r1, mask
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@ -296,6 +359,7 @@ n2hend: ret
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space: data 20
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prompt: data 3e
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plus: data 2b
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minus: data 2d
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equals: data 3d
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qmark: data 3f
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backsp: data 8
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@ -357,6 +421,7 @@ tbl29: data 65
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tbl2a: data f
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tbl2b: data 66
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;First argument
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;Variables
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ovrflw: data 0
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arg1: data 0
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sign: data 0
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