Anachronaut
e1273337c4
Twenty four places moved Q into A or B by pushing it and popping it back. That is four bus cycles and two bytes to do what MVQA does in one of each, and several of them are inside loops - Life, the calculator, int8. Nineteen more loaded zero with INIA 0d0 where RSTA says the same thing in one byte. Both are equivalent at the CPU rather than by assertion: RSTA and INIA both leave Status alone, and PSHQ followed by POPA nets to A = Q with the Stack Pointer where it started. The one difference is that the pair leaves a copy of Q in memory just below the Stack Pointer and MVQA does not, which nothing here reads. Five recorded outputs moved and every one of them says the change worked: - 16x16Life fits five more generations into the same cycle budget, the first 457 lines identical, because the loop got cheaper. - Life.sbx is 1409 bytes rather than 1411, in three tests that list it. - Edit.sbx is 1995 rather than 1996. That last one broke a check I added this morning, and the hole is worth recording: the CosmOS README's claim about Edit's size did not have the word "Edit" on the same line as the number, because the subject was in the sentence before, so the check that measures quoted sizes skipped it silently. The sentence now names what it is talking about, which makes it both checkable and clearer, and the check fails on a wrong number there. Comments on either half of a replaced pair are carried onto the instruction that replaces them, so nothing anybody wrote was lost.
85 lines
2.6 KiB
NASM
85 lines
2.6 KiB
NASM
; This file supplies basic support for int8 values.
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#Program
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; Basic int8 subroutines.
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; An int8 value is an 8 bit unsigned integer. Just a byte literally interpreted as a value.
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; Basic operations on int8 values use A and B as operands with the result returned in Q, similar to the bare arithmetic instructions of SplitBit.
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int8mult:
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; Multiply A by B and return the result in Q.
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; This subroutine is limited to outputs in the range of 0-255.
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; It does not reliably return with the Carry Flag set if the result is too large to fit in the range.
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; First, check if either is zero, and if so, return zero.
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BRB return0
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BRA return0
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PSHB ; Push the multiplier to the stack.
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PSHA ; Push the multiplicand to the stack.
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POPB ; Pop the multiplicand into B.
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RSTA ; Set A to 0.
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CCF ; Clear the Carry Flag, just in case.
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int8multLoop:
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ADD ; Add the multiplicand to A.
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POPA ; Pop the multiplier into A.
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DECA ; Subtract one from the multiplier.
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BRA int8multDone ; If the multiplier becomes zero, we're done.
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PSHA ; Push the multiplier back to the stack.
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MVQA ; Push the running total to the stack. Pop the running total into A.
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BRI int8multLoop
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return0:
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RSTA
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RSTB
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ADD
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int8multDone:
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RET
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int8div:
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; Divide A by B and return the quotient in Q.
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; First, check if either A or B are 0, if so, return 0.
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BRB return0
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BRA return0
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; This dance of pushes, pops, and addition creates a quotient counter on the Stack while preserving A and B.
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PSHA ; Push A to the Stack.
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PSHB ; Push B to the Stack.
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RSTA ; Set A and B to 0.
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RSTB
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ADD ; Add them together, setting Q to 0.
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POPB ; Restore B.
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POPA ; Restore A.
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PSHQ ; Push a 0 onto the Stack.
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; The Carry Flag is clear and we can proceed with the division.
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int8divLoop:
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SUB ; Subtract B from A.
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; If we generate a carry we're done.
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BRC int8divDone
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; Otherwise, increment the quotient counter and subtract again.
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POPA ; Pop the quotient counter from the stack.
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INCA ; Increment it.
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PSHA ; Push it back onto the stack.
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MVQA ; Push the running total onto the stack. Pop the runing total into A.
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BRI int8divLoop ; Branch back to the loop.
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int8divDone:
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CCF ; Clear the Carry Flag.
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POPA ; Pop the quotient into A.
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RSTB ; Set B to 0.
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ADD ; Add them together to move the result to Q.
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RET ; Return to the caller.
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int8mod:
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; Divide A by B and return the remainder in Q.
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; If A or B are 0, return 0.
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BRB return0
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BRA return0
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int8modLoop:
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SUB ; Subtract B from A.
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BRC int8modDone
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MVQA
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BRI int8modLoop
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int8modDone:
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; Add the divisor to Q to get the remainder.
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CCF
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MVQA
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ADD
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RET
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