f6a1e08218
My i386 code from 893df4b gave the wrong sign to some 8-byte
remainders. Fix by splitting .dvi8 and .rmi8 so each has its own code
to pick the sign. They and .dvu8 and .rmu8 share a private sub
.divrem8 for unsigned division.
Improve the i386 code by using instructions like _bsr_ and _shrd_.
Change the helpers to yield a quotient in ebx:eax or a remainder in
ecx:edx; this seems more convenient, because _div_ puts its quotient
in eax and remainder in edx.
38 lines
784 B
ArmAsm
38 lines
784 B
ArmAsm
.sect .text; .sect .rom; .sect .data; .sect .bss
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.sect .text
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.define .dvi8
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yl=4
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yh=8
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xl=12
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xh=16
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! .dvi8 yields ebx:eax = quotient from x / y
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.dvi8:
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xorb cl,cl ! cl = 0, non-negative result
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mov eax,xh(esp) ! eax for .divrem8
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test eax,eax
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jge 1f ! jump unless x < 0
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incb cl ! cl = 1, negative result
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neg eax
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neg xl(esp)
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sbb eax,0
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mov xh(esp),eax ! x = absolute value
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1: mov edx,yh(esp) ! edx for .divrem8
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test edx,edx ! flag z for .divrem8 when y >= 0
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jge 1f ! jump unless y < 0
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xorb cl,1 ! flip sign of result
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neg edx
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neg yl(esp)
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sbb edx,0 ! flag z for .divrem8 when y < 0
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mov yh(esp),edx ! y = absolute value
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1: push ecx
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call .divrem8
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pop ecx
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testb cl,cl
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jz 1f ! jump unless result < 0
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neg ebx
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neg eax
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sbb ebx,0 ! negate quotient ebx:eax
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1: ret 16
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