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COMMENT This routine is used in more than one place, and is essentially a template that can by used for many different types, eg INT, LONG INT... USAGE MODE POWMODSTRUCT = INT, LONG INT, COMPL, FRAC, MODULAS, MATRIX etc PR READ "prelude/pow_mod.a68" PR END COMMENT
PROC pow mod = (POWMODSTRUCT b,in e, mod)POWMODSTRUCT: (
POWMODSTRUCT sq := b, e := in e;
POWMODSTRUCT out:= IF ODD e THEN b ELSE 1 FI;
e:=e OVER 2;
WHILE e /= 0 DO
sq := sq * sq %* mod;
IF ODD e THEN out := out * sq %* mod FI ;
e:=e OVER 2
OD;
out
)