[Cyan]<Cedar6.0>TJaM>TJaMHashImpl.mesa!1

TJaMHashImpl.mesa

Doug Wyatt, 1-Oct-81 13:43:53

Russ Atkinson, July 22, 1983 6:18 pm

Michael Plass, February 14, 1985 12:39:04 pm PST

DIRECTORY

Basics USING [BITSHIFT, BITXOR, HighHalf, LowHalf],

TJaMBasic USING [Object],

TJaMDict USING [],

TJaMVM USING [GetText];

TJaMHashImpl: PROGRAM

IMPORTS TJaMVM, Basics

EXPORTS TJaMDict = {

HashObject: PUBLIC PROC[key: TJaMBasic.Object] RETURNS[CARDINAL] = {

hashes object key into a CARDINAL

Expects caller to do: (h MOD range) to allow for different ranges with same key

WITH k: key SELECT FROM

integer => RETURN[Basics.LowHalf[k.ivalue]];

real => RETURN[Basics.HighHalf[LOOPHOLE[k.rvalue]]];

boolean => RETURN[LOOPHOLE[k.bvalue]];

name => RETURN[k.id.index];

string => RETURN[HashString[k]];

stream => RETURN[k.index];

command => RETURN[k.index];

ENDCASE => RETURN[0];

};

HashString and HashText must be consistent!

maxLength: CARDINAL = 20;

HashString: PUBLIC PROC[s: string TJaMBasic.Object] RETURNS[CARDINAL] = {

text: STRING ← [maxLength]; TJaMVM.GetText[s,text];

RETURN[InlineHash[text,s.length]]

};

HashText: PUBLIC PROC[text: LONG STRING] RETURNS[CARDINAL] = {

RETURN[InlineHash[text,text.length]]

};

InlineHash: PROC[text: LONG STRING, h: CARDINAL] RETURNS[CARDINAL] = INLINE {

len: CARDINAL ← MIN[text.length,maxLength];

FOR i: CARDINAL IN[1..MIN[3,len]) DO

h ← Basics.BITXOR[Basics.BITSHIFT[h,1], LOOPHOLE[text[i]]];

ENDLOOP;

IF len >= 2 THEN FOR i: CARDINAL IN[len - 2..len) DO

h ← Basics.BITXOR[Basics.BITSHIFT[h,1], LOOPHOLE[text[i]]];

ENDLOOP;

RETURN[h];

};