<<>> <> <> <> <> <> <> <> <> DIRECTORY Basics USING [LongNumber, BITAND, BITOR, BITSHIFT], Ieee USING [ExponentBias, ExpSingleMax, ExpSingleMin, HiFractionMask, NaNExponent, SingleReal], Real USING [PlusZero], RealConvert USING [BcplReal]; RealConvertImpl: PROGRAM IMPORTS Basics EXPORTS RealConvert = BEGIN OPEN Basics, RealConvert; BcplHiddenBit: CARDINAL = 200B; BcplBiasDifference: INTEGER = 1; -- Bias difference MesaBiasDifference: INTEGER = 2; MaxBiasedExponent: INTEGER = Ieee.ExpSingleMax + Ieee.ExponentBias; MinBiasedExponent: INTEGER = Ieee.ExpSingleMin + Ieee.ExponentBias; MostNegativeBcpl: LONG INTEGER = FIRST[LONG INTEGER]; MostPositiveBcpl: LONG INTEGER = LAST[LONG INTEGER]; CVError: PUBLIC SAFE ERROR = CODE; BitOn: PROC [a, b: WORD] RETURNS [BOOL] = INLINE { RETURN[BITAND[a, b] # 0]; }; <> <> <<-- first convert to sign magnitude>> <> <> <> <> <> <> <<-- Need to denormalize!>> <> <> <> <> <> <> <> <> <<} -- Bias the exponent>> <> <> <<};>> <<>> SwapHalves: PROC [n: CARD32] RETURNS [CARD32] ~ INLINE { RETURN[(n * 2**16) + (n / 2**16)]; }; BcplToIeee: PUBLIC SAFE PROC [a: BcplReal] RETURNS [b: REAL] = TRUSTED { fl: Ieee.SingleReal ¬ LOOPHOLE[SwapHalves[LOOPHOLE[a]]]; frac: LongNumber; exp: INTEGER; IF fl.sign THEN { fl ¬ LOOPHOLE[-LOOPHOLE[fl, LONG INTEGER], Ieee.SingleReal]; fl.sign ¬ TRUE; }; exp ¬ fl.exp; frac ¬ LOOPHOLE[fl, LongNumber]; frac.hi ¬ BITAND[frac.hi, Ieee.HiFractionMask]; IF frac.lc = 0 THEN RETURN[Real.PlusZero]; <> WHILE NOT BitOn[frac.hi, BcplHiddenBit] DO exp ¬ exp - 1; frac.lc ¬ frac.lc+frac.lc; -- Bias the exponent ENDLOOP; exp ¬ exp - BcplBiasDifference; SELECT exp FROM < MinBiasedExponent => { THROUGH [exp..MinBiasedExponent) DO frac.lc ¬ frac.lc/2; ENDLOOP; exp ¬ 0; }; IN [MinBiasedExponent..MaxBiasedExponent] => NULL; ENDCASE => ERROR; fl.m ¬ BITOR[BITSHIFT[BITAND[frac.hi, Ieee.HiFractionMask], 16], frac.lo]; fl.exp ¬ exp; RETURN[LOOPHOLE[fl, REAL]]; }; IeeeToBcpl: PUBLIC SAFE PROC [a: REAL] RETURNS [BcplReal] = TRUSTED { fl: Ieee.SingleReal ¬ LOOPHOLE[a, Ieee.SingleReal]; sign: BOOL ¬ fl.sign; frac: LongNumber; exp: INTEGER ¬ fl.exp; IF fl.exp = Ieee.NaNExponent + Ieee.ExponentBias AND (fl.m # 0) THEN ERROR CVError[]; fl.sign ¬ FALSE; frac ¬ LOOPHOLE[fl, LongNumber]; IF frac.lc = 0 THEN RETURN[[0]]; frac.hi ¬ BITAND[frac.hi, Ieee.HiFractionMask]; SELECT exp FROM < MinBiasedExponent => { <> <> exp ¬ exp + 1; WHILE NOT BitOn[frac.hi, BcplHiddenBit] DO exp ¬ exp - 1; frac.lc ¬ frac.lc*2; ENDLOOP; frac.lc ¬ frac.lc/2; exp ¬ exp + MesaBiasDifference; -- Denormalize WHILE exp < 0 DO exp ¬ exp + 1; frac.lc ¬ frac.lc/2; ENDLOOP; }; ENDCASE => { frac.hi ¬ frac.hi + BcplHiddenBit; <> IF BitOn[frac.lo, 1] AND BitOn[frac.lo, 2] THEN frac.lc ¬ frac.lc + 1; frac.lc ¬ frac.lc/2; exp ¬ exp + MesaBiasDifference; IF BitOn[frac.hi, BcplHiddenBit] THEN { exp ¬ exp + 1; frac.lc ¬ frac.lc/2; }; IF exp > 377B THEN RETURN[LOOPHOLE[SwapHalves[LOOPHOLE[IF fl.sign THEN MostNegativeBcpl ELSE MostPositiveBcpl]]]]; }; fl.m ¬ BITOR[BITSHIFT[BITAND[frac.hi, Ieee.HiFractionMask], 16], frac.lo]; fl.exp ¬ exp; IF sign THEN fl ¬ LOOPHOLE[-LOOPHOLE[fl, INT], Ieee.SingleReal]; RETURN[LOOPHOLE[SwapHalves[LOOPHOLE[fl]]]]; }; END. L. Stewart August 13, 1980 3:17 PM modified from RealConvert.mesa L. Stewart August 14, 1980 3:30 PM added BcplToIeee L. Stewart August 15, 1980 12:31 PM fixes to BcplToIeee August 25, 1980 1:17 PM, LStewart; added IeeeToBcpl August 27, 1982 1:21 pm, L. Stewart; SAFE January 14, 1984 5:04 pm, Stewart, change to Ieee