------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- E V A L _ F A T -- -- -- -- B o d y -- -- -- -- -- -- Copyright (C) 1992-2001 Free Software Foundation, Inc. -- -- -- -- GNAT is free software; you can redistribute it and/or modify it under -- -- terms of the GNU General Public License as published by the Free Soft- -- -- ware Foundation; either version 2, or (at your option) any later ver- -- -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- -- for more details. You should have received a copy of the GNU General -- -- Public License distributed with GNAT; see file COPYING. If not, write -- -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, -- -- MA 02111-1307, USA. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ with Einfo; use Einfo; with Sem_Util; use Sem_Util; with Ttypef; use Ttypef; with Targparm; use Targparm; package body Eval_Fat is Radix : constant Int := 2; -- This code is currently only correct for the radix 2 case. We use -- the symbolic value Radix where possible to help in the unlikely -- case of anyone ever having to adjust this code for another value, -- and for documentation purposes. type Radix_Power_Table is array (Int range 1 .. 4) of Int; Radix_Powers : constant Radix_Power_Table := (Radix**1, Radix**2, Radix**3, Radix**4); function Float_Radix return T renames Ureal_2; -- Radix expressed in real form ----------------------- -- Local Subprograms -- ----------------------- procedure Decompose (RT : R; X : in T; Fraction : out T; Exponent : out UI; Mode : Rounding_Mode := Round); -- Decomposes a non-zero floating-point number into fraction and -- exponent parts. The fraction is in the interval 1.0 / Radix .. -- T'Pred (1.0) and uses Rbase = Radix. -- The result is rounded to a nearest machine number. procedure Decompose_Int (RT : R; X : in T; Fraction : out UI; Exponent : out UI; Mode : Rounding_Mode); -- This is similar to Decompose, except that the Fraction value returned -- is an integer representing the value Fraction * Scale, where Scale is -- the value (Radix ** Machine_Mantissa (RT)). The value is obtained by -- using biased rounding (halfway cases round away from zero), round to -- even, a floor operation or a ceiling operation depending on the setting -- of Mode (see corresponding descriptions in Urealp). -- In case rounding was specified, Rounding_Was_Biased is set True -- if the input was indeed halfway between to machine numbers and -- got rounded away from zero to an odd number. function Eps_Model (RT : R) return T; -- Return the smallest model number of R. function Eps_Denorm (RT : R) return T; -- Return the smallest denormal of type R. function Machine_Mantissa (RT : R) return Nat; -- Get value of machine mantissa -------------- -- Adjacent -- -------------- function Adjacent (RT : R; X, Towards : T) return T is begin if Towards = X then return X; elsif Towards > X then return Succ (RT, X); else return Pred (RT, X); end if; end Adjacent; ------------- -- Ceiling -- ------------- function Ceiling (RT : R; X : T) return T is XT : constant T := Truncation (RT, X); begin if UR_Is_Negative (X) then return XT; elsif X = XT then return X; else return XT + Ureal_1; end if; end Ceiling; ------------- -- Compose -- ------------- function Compose (RT : R; Fraction : T; Exponent : UI) return T is Arg_Frac : T; Arg_Exp : UI; begin if UR_Is_Zero (Fraction) then return Fraction; else Decompose (RT, Fraction, Arg_Frac, Arg_Exp); return Scaling (RT, Arg_Frac, Exponent); end if; end Compose; --------------- -- Copy_Sign -- --------------- function Copy_Sign (RT : R; Value, Sign : T) return T is pragma Warnings (Off, RT); Result : T; begin Result := abs Value; if UR_Is_Negative (Sign) then return -Result; else return Result; end if; end Copy_Sign; --------------- -- Decompose -- --------------- procedure Decompose (RT : R; X : in T; Fraction : out T; Exponent : out UI; Mode : Rounding_Mode := Round) is Int_F : UI; begin Decompose_Int (RT, abs X, Int_F, Exponent, Mode); Fraction := UR_From_Components (Num => Int_F, Den => UI_From_Int (Machine_Mantissa (RT)), Rbase => Radix, Negative => False); if UR_Is_Negative (X) then Fraction := -Fraction; end if; return; end Decompose; ------------------- -- Decompose_Int -- ------------------- -- This procedure should be modified with care, as there -- are many non-obvious details that may cause problems -- that are hard to detect. The cases of positive and -- negative zeroes are also special and should be -- verified separately. procedure Decompose_Int (RT : R; X : in T; Fraction : out UI; Exponent : out UI; Mode : Rounding_Mode) is Base : Int := Rbase (X); N : UI := abs Numerator (X); D : UI := Denominator (X); N_Times_Radix : UI; Even : Boolean; -- True iff Fraction is even Most_Significant_Digit : constant UI := Radix ** (Machine_Mantissa (RT) - 1); Uintp_Mark : Uintp.Save_Mark; -- The code is divided into blocks that systematically release -- intermediate values (this routine generates lots of junk!) begin Calculate_D_And_Exponent_1 : begin Uintp_Mark := Mark; Exponent := Uint_0; -- In cases where Base > 1, the actual denominator is -- Base**D. For cases where Base is a power of Radix, use -- the value 1 for the Denominator and adjust the exponent. -- Note: Exponent has different sign from D, because D is a divisor for Power in 1 .. Radix_Powers'Last loop if Base = Radix_Powers (Power) then Exponent := -D * Power; Base := 0; D := Uint_1; exit; end if; end loop; Release_And_Save (Uintp_Mark, D, Exponent); end Calculate_D_And_Exponent_1; if Base > 0 then Calculate_Exponent : begin Uintp_Mark := Mark; -- For bases that are a multiple of the Radix, divide -- the base by Radix and adjust the Exponent. This will -- help because D will be much smaller and faster to process. -- This occurs for decimal bases on a machine with binary -- floating-point for example. When calculating 1E40, -- with Radix = 2, N will be 93 bits instead of 133. -- N E -- ------ * Radix -- D -- Base -- N E -- = -------------------------- * Radix -- D D -- (Base/Radix) * Radix -- N E-D -- = --------------- * Radix -- D -- (Base/Radix) -- This code is commented out, because it causes numerous -- failures in the regression suite. To be studied ??? while False and then Base > 0 and then Base mod Radix = 0 loop Base := Base / Radix; Exponent := Exponent + D; end loop; Release_And_Save (Uintp_Mark, Exponent); end Calculate_Exponent; -- For remaining bases we must actually compute -- the exponentiation. -- Because the exponentiation can be negative, and D must -- be integer, the numerator is corrected instead. Calculate_N_And_D : begin Uintp_Mark := Mark; if D < 0 then N := N * Base ** (-D); D := Uint_1; else D := Base ** D; end if; Release_And_Save (Uintp_Mark, N, D); end Calculate_N_And_D; Base := 0; end if; -- Now scale N and D so that N / D is a value in the -- interval [1.0 / Radix, 1.0) and adjust Exponent accordingly, -- so the value N / D * Radix ** Exponent remains unchanged. -- Step 1 - Adjust N so N / D >= 1 / Radix, or N = 0 -- N and D are positive, so N / D >= 1 / Radix implies N * Radix >= D. -- This scaling is not possible for N is Uint_0 as there -- is no way to scale Uint_0 so the first digit is non-zero. Calculate_N_And_Exponent : begin Uintp_Mark := Mark; N_Times_Radix := N * Radix; if N /= Uint_0 then while not (N_Times_Radix >= D) loop N := N_Times_Radix; Exponent := Exponent - 1; N_Times_Radix := N * Radix; end loop; end if; Release_And_Save (Uintp_Mark, N, Exponent); end Calculate_N_And_Exponent; -- Step 2 - Adjust D so N / D < 1 -- Scale up D so N / D < 1, so N < D Calculate_D_And_Exponent_2 : begin Uintp_Mark := Mark; while not (N < D) loop -- As N / D >= 1, N / (D * Radix) will be at least 1 / Radix, -- so the result of Step 1 stays valid D := D * Radix; Exponent := Exponent + 1; end loop; Release_And_Save (Uintp_Mark, D, Exponent); end Calculate_D_And_Exponent_2; -- Here the value N / D is in the range [1.0 / Radix .. 1.0) -- Now find the fraction by doing a very simple-minded -- division until enough digits have been computed. -- This division works for all radices, but is only efficient for -- a binary radix. It is just like a manual division algorithm, -- but instead of moving the denominator one digit right, we move -- the numerator one digit left so the numerator and denominator -- remain integral. Fraction := Uint_0; Even := True; Calculate_Fraction_And_N : begin Uintp_Mark := Mark; loop while N >= D loop N := N - D; Fraction := Fraction + 1; Even := not Even; end loop; -- Stop when the result is in [1.0 / Radix, 1.0) exit when Fraction >= Most_Significant_Digit; N := N * Radix; Fraction := Fraction * Radix; Even := True; end loop; Release_And_Save (Uintp_Mark, Fraction, N); end Calculate_Fraction_And_N; Calculate_Fraction_And_Exponent : begin Uintp_Mark := Mark; -- Put back sign before applying the rounding. if UR_Is_Negative (X) then Fraction := -Fraction; end if; -- Determine correct rounding based on the remainder -- which is in N and the divisor D. Rounding_Was_Biased := False; -- Until proven otherwise case Mode is when Round_Even => -- This rounding mode should not be used for static -- expressions, but only for compile-time evaluation -- of non-static expressions. if (Even and then N * 2 > D) or else (not Even and then N * 2 >= D) then Fraction := Fraction + 1; end if; when Round => -- Do not round to even as is done with IEEE arithmetic, -- but instead round away from zero when the result is -- exactly between two machine numbers. See RM 4.9(38). if N * 2 >= D then Fraction := Fraction + 1; Rounding_Was_Biased := Even and then N * 2 = D; -- Check for the case where the result is actually -- different from Round_Even. end if; when Ceiling => if N > Uint_0 then Fraction := Fraction + 1; end if; when Floor => null; end case; -- The result must be normalized to [1.0/Radix, 1.0), -- so adjust if the result is 1.0 because of rounding. if Fraction = Most_Significant_Digit * Radix then Fraction := Most_Significant_Digit; Exponent := Exponent + 1; end if; Release_And_Save (Uintp_Mark, Fraction, Exponent); end Calculate_Fraction_And_Exponent; end Decompose_Int; ---------------- -- Eps_Denorm -- ---------------- function Eps_Denorm (RT : R) return T is Digs : constant UI := Digits_Value (RT); Emin : Int; Mant : Int; begin if Vax_Float (RT) then if Digs = VAXFF_Digits then Emin := VAXFF_Machine_Emin; Mant := VAXFF_Machine_Mantissa; elsif Digs = VAXDF_Digits then Emin := VAXDF_Machine_Emin; Mant := VAXDF_Machine_Mantissa; else pragma Assert (Digs = VAXGF_Digits); Emin := VAXGF_Machine_Emin; Mant := VAXGF_Machine_Mantissa; end if; elsif Is_AAMP_Float (RT) then if Digs = AAMPS_Digits then Emin := AAMPS_Machine_Emin; Mant := AAMPS_Machine_Mantissa; else pragma Assert (Digs = AAMPL_Digits); Emin := AAMPL_Machine_Emin; Mant := AAMPL_Machine_Mantissa; end if; else if Digs = IEEES_Digits then Emin := IEEES_Machine_Emin; Mant := IEEES_Machine_Mantissa; elsif Digs = IEEEL_Digits then Emin := IEEEL_Machine_Emin; Mant := IEEEL_Machine_Mantissa; else pragma Assert (Digs = IEEEX_Digits); Emin := IEEEX_Machine_Emin; Mant := IEEEX_Machine_Mantissa; end if; end if; return Float_Radix ** UI_From_Int (Emin - Mant); end Eps_Denorm; --------------- -- Eps_Model -- --------------- function Eps_Model (RT : R) return T is Digs : constant UI := Digits_Value (RT); Emin : Int; begin if Vax_Float (RT) then if Digs = VAXFF_Digits then Emin := VAXFF_Machine_Emin; elsif Digs = VAXDF_Digits then Emin := VAXDF_Machine_Emin; else pragma Assert (Digs = VAXGF_Digits); Emin := VAXGF_Machine_Emin; end if; elsif Is_AAMP_Float (RT) then if Digs = AAMPS_Digits then Emin := AAMPS_Machine_Emin; else pragma Assert (Digs = AAMPL_Digits); Emin := AAMPL_Machine_Emin; end if; else if Digs = IEEES_Digits then Emin := IEEES_Machine_Emin; elsif Digs = IEEEL_Digits then Emin := IEEEL_Machine_Emin; else pragma Assert (Digs = IEEEX_Digits); Emin := IEEEX_Machine_Emin; end if; end if; return Float_Radix ** UI_From_Int (Emin); end Eps_Model; -------------- -- Exponent -- -------------- function Exponent (RT : R; X : T) return UI is X_Frac : UI; X_Exp : UI; begin if UR_Is_Zero (X) then return Uint_0; else Decompose_Int (RT, X, X_Frac, X_Exp, Round_Even); return X_Exp; end if; end Exponent; ----------- -- Floor -- ----------- function Floor (RT : R; X : T) return T is XT : constant T := Truncation (RT, X); begin if UR_Is_Positive (X) then return XT; elsif XT = X then return X; else return XT - Ureal_1; end if; end Floor; -------------- -- Fraction -- -------------- function Fraction (RT : R; X : T) return T is X_Frac : T; X_Exp : UI; begin if UR_Is_Zero (X) then return X; else Decompose (RT, X, X_Frac, X_Exp); return X_Frac; end if; end Fraction; ------------------ -- Leading_Part -- ------------------ function Leading_Part (RT : R; X : T; Radix_Digits : UI) return T is L : UI; Y, Z : T; begin if Radix_Digits >= Machine_Mantissa (RT) then return X; else L := Exponent (RT, X) - Radix_Digits; Y := Truncation (RT, Scaling (RT, X, -L)); Z := Scaling (RT, Y, L); return Z; end if; end Leading_Part; ------------- -- Machine -- ------------- function Machine (RT : R; X : T; Mode : Rounding_Mode) return T is X_Frac : T; X_Exp : UI; begin if UR_Is_Zero (X) then return X; else Decompose (RT, X, X_Frac, X_Exp, Mode); return Scaling (RT, X_Frac, X_Exp); end if; end Machine; ---------------------- -- Machine_Mantissa -- ---------------------- function Machine_Mantissa (RT : R) return Nat is Digs : constant UI := Digits_Value (RT); Mant : Nat; begin if Vax_Float (RT) then if Digs = VAXFF_Digits then Mant := VAXFF_Machine_Mantissa; elsif Digs = VAXDF_Digits then Mant := VAXDF_Machine_Mantissa; else pragma Assert (Digs = VAXGF_Digits); Mant := VAXGF_Machine_Mantissa; end if; elsif Is_AAMP_Float (RT) then if Digs = AAMPS_Digits then Mant := AAMPS_Machine_Mantissa; else pragma Assert (Digs = AAMPL_Digits); Mant := AAMPL_Machine_Mantissa; end if; else if Digs = IEEES_Digits then Mant := IEEES_Machine_Mantissa; elsif Digs = IEEEL_Digits then Mant := IEEEL_Machine_Mantissa; else pragma Assert (Digs = IEEEX_Digits); Mant := IEEEX_Machine_Mantissa; end if; end if; return Mant; end Machine_Mantissa; ----------- -- Model -- ----------- function Model (RT : R; X : T) return T is X_Frac : T; X_Exp : UI; begin Decompose (RT, X, X_Frac, X_Exp); return Compose (RT, X_Frac, X_Exp); end Model; ---------- -- Pred -- ---------- function Pred (RT : R; X : T) return T is Result_F : UI; Result_X : UI; begin if abs X < Eps_Model (RT) then if Denorm_On_Target then return X - Eps_Denorm (RT); elsif X > Ureal_0 then -- Target does not support denorms, so predecessor is 0.0 return Ureal_0; else -- Target does not support denorms, and X is 0.0 -- or at least bigger than -Eps_Model (RT) return -Eps_Model (RT); end if; else Decompose_Int (RT, X, Result_F, Result_X, Ceiling); return UR_From_Components (Num => Result_F - 1, Den => Machine_Mantissa (RT) - Result_X, Rbase => Radix, Negative => False); -- Result_F may be false, but this is OK as UR_From_Components -- handles that situation. end if; end Pred; --------------- -- Remainder -- --------------- function Remainder (RT : R; X, Y : T) return T is A : T; B : T; Arg : T; P : T; Arg_Frac : T; P_Frac : T; Sign_X : T; IEEE_Rem : T; Arg_Exp : UI; P_Exp : UI; K : UI; P_Even : Boolean; begin if UR_Is_Positive (X) then Sign_X := Ureal_1; else Sign_X := -Ureal_1; end if; Arg := abs X; P := abs Y; if Arg < P then P_Even := True; IEEE_Rem := Arg; P_Exp := Exponent (RT, P); else -- ??? what about zero cases? Decompose (RT, Arg, Arg_Frac, Arg_Exp); Decompose (RT, P, P_Frac, P_Exp); P := Compose (RT, P_Frac, Arg_Exp); K := Arg_Exp - P_Exp; P_Even := True; IEEE_Rem := Arg; for Cnt in reverse 0 .. UI_To_Int (K) loop if IEEE_Rem >= P then P_Even := False; IEEE_Rem := IEEE_Rem - P; else P_Even := True; end if; P := P * Ureal_Half; end loop; end if; -- That completes the calculation of modulus remainder. The final step -- is get the IEEE remainder. Here we compare Rem with (abs Y) / 2. if P_Exp >= 0 then A := IEEE_Rem; B := abs Y * Ureal_Half; else A := IEEE_Rem * Ureal_2; B := abs Y; end if; if A > B or else (A = B and then not P_Even) then IEEE_Rem := IEEE_Rem - abs Y; end if; return Sign_X * IEEE_Rem; end Remainder; -------------- -- Rounding -- -------------- function Rounding (RT : R; X : T) return T is Result : T; Tail : T; begin Result := Truncation (RT, abs X); Tail := abs X - Result; if Tail >= Ureal_Half then Result := Result + Ureal_1; end if; if UR_Is_Negative (X) then return -Result; else return Result; end if; end Rounding; ------------- -- Scaling -- ------------- function Scaling (RT : R; X : T; Adjustment : UI) return T is pragma Warnings (Off, RT); begin if Rbase (X) = Radix then return UR_From_Components (Num => Numerator (X), Den => Denominator (X) - Adjustment, Rbase => Radix, Negative => UR_Is_Negative (X)); elsif Adjustment >= 0 then return X * Radix ** Adjustment; else return X / Radix ** (-Adjustment); end if; end Scaling; ---------- -- Succ -- ---------- function Succ (RT : R; X : T) return T is Result_F : UI; Result_X : UI; begin if abs X < Eps_Model (RT) then if Denorm_On_Target then return X + Eps_Denorm (RT); elsif X < Ureal_0 then -- Target does not support denorms, so successor is 0.0 return Ureal_0; else -- Target does not support denorms, and X is 0.0 -- or at least smaller than Eps_Model (RT) return Eps_Model (RT); end if; else Decompose_Int (RT, X, Result_F, Result_X, Floor); return UR_From_Components (Num => Result_F + 1, Den => Machine_Mantissa (RT) - Result_X, Rbase => Radix, Negative => False); -- Result_F may be false, but this is OK as UR_From_Components -- handles that situation. end if; end Succ; ---------------- -- Truncation -- ---------------- function Truncation (RT : R; X : T) return T is pragma Warnings (Off, RT); begin return UR_From_Uint (UR_Trunc (X)); end Truncation; ----------------------- -- Unbiased_Rounding -- ----------------------- function Unbiased_Rounding (RT : R; X : T) return T is Abs_X : constant T := abs X; Result : T; Tail : T; begin Result := Truncation (RT, Abs_X); Tail := Abs_X - Result; if Tail > Ureal_Half then Result := Result + Ureal_1; elsif Tail = Ureal_Half then Result := Ureal_2 * Truncation (RT, (Result / Ureal_2) + Ureal_Half); end if; if UR_Is_Negative (X) then return -Result; elsif UR_Is_Positive (X) then return Result; -- For zero case, make sure sign of zero is preserved else return X; end if; end Unbiased_Rounding; end Eval_Fat;