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PDP-10 Archives
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decuslib10-05
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43,50337/23/bitfie.mac
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COMMENT * SIMULA specification;
OPTIONS(/E:QUICK,bitfield);
INTEGER PROCEDURE bitfield(w,firstbit,len);
INTEGER w,firstbit,len;
COMMENT Returns the byte starting at firstbit (0-35) of length len bits.
len>=0 AND len<36 AND firstbit+len<=36 must hold.
Special option: IF len<0, use -len and extend sign bit.
;
!*;! MACRO-10 code !*;!
TITLE bitfield
ENTRY bitfield
SUBTTL SIMULA utility, Lars Enderin April 1976
;!*** Copyright 1976 by the Swedish Defence Research Institute. ***
;!*** Copying is allowed. ***
sall
search simmac,simmcr,simrpa
macinit
;! Local definitions ;!
w==0
firstbit==1
len==2
bitfield:
PROC
L w(XTAC)
L X1,firstbit(XTAC)
LSH (X1)
L X1,len(XTAC)
IF ;! Positive len
JUMPL X1,FALSE
THEN ;! Do not propagate sign
LSH -^d36(X1)
ELSE ;! Extend sign bit to the left
MOVNI X1,^d36(X1)
ASH (X1)
FI
ST (XTAC)
RETURN
EPROC
LIT
END;