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Tricks of the Windows Gam…ming Gurus (2nd Edition)
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llshr.asm
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Assembly Source File
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1998-06-17
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2KB
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81 lines
title llshr - long shift right
;***
;llshr.asm - long shift right
;
; Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
;
;Purpose:
; define signed long shift right routine
; __allshr
;
;*******************************************************************************
.xlist
include cruntime.inc
include mm.inc
.list
;***
;llshr - long shift right
;
;Purpose:
; Does a signed Long Shift Right
; Shifts a long right any number of bits.
;
;Entry:
; EDX:EAX - long value to be shifted
; CL - number of bits to shift by
;
;Exit:
; EDX:EAX - shifted value
;
;Uses:
; CL is destroyed.
;
;Exceptions:
;
;*******************************************************************************
CODESEG
_allshr PROC NEAR
;
; Handle shifts of 64 bits or more (if shifting 64 bits or more, the result
; depends only on the high order bit of edx).
;
cmp cl,64
jae short RETSIGN
;
; Handle shifts of between 0 and 31 bits
;
cmp cl, 32
jae short MORE32
shrd eax,edx,cl
sar edx,cl
ret
;
; Handle shifts of between 32 and 63 bits
;
MORE32:
mov eax,edx
sar edx,31
and cl,31
sar eax,cl
ret
;
; Return double precision 0 or -1, depending on the sign of edx
;
RETSIGN:
sar edx,31
mov eax,edx
ret
_allshr ENDP
end