diff options
author | Eric Botcazou <ebotcazou@adacore.com> | 2020-11-19 15:35:35 +0100 |
---|---|---|
committer | Pierre-Marie de Rodat <derodat@adacore.com> | 2020-12-14 10:51:52 -0500 |
commit | f3dd0581a51be1e4354bdcf23f1eee7f5c707a3a (patch) | |
tree | 4ff2a0588200a32fe7e68f97b7769bb10835a810 /gcc | |
parent | 3cde9f1cc56d7039f44d3cd4f4ebebd02815b8a9 (diff) | |
download | gcc-f3dd0581a51be1e4354bdcf23f1eee7f5c707a3a.zip gcc-f3dd0581a51be1e4354bdcf23f1eee7f5c707a3a.tar.gz gcc-f3dd0581a51be1e4354bdcf23f1eee7f5c707a3a.tar.bz2 |
[Ada] Implement part of System.Fat_Gen more efficiently
gcc/ada/
* libgnat/s-fatgen.ads (Compose): Add pragma Inline.
(Copy_Sign): Likewise.
(Exponent): Likewise.
(Fraction): Likewise.
* libgnat/s-fatgen.adb: Remove with clause for System, add
with and use clauses for System.Unsigned_Types.
Add pragma Warnings (Off) for non-static constants.
Remove precomputed tables of powers of radix and add a few
constants describing the floating-point format.
(Gradual_Scaling): Delete.
(Copy_Sign): Reimplement directly.
(Decompose): Likewise.
(Scaling): Likewise.
(Pred): Speed up.
(Succ): Likewise.
(Truncation): Tidy up.
(Valid): Move constants to library level.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/ada/libgnat/s-fatgen.adb | 587 | ||||
-rw-r--r-- | gcc/ada/libgnat/s-fatgen.ads | 9 |
2 files changed, 267 insertions, 329 deletions
diff --git a/gcc/ada/libgnat/s-fatgen.adb b/gcc/ada/libgnat/s-fatgen.adb index e590198..bebe737 100644 --- a/gcc/ada/libgnat/s-fatgen.adb +++ b/gcc/ada/libgnat/s-fatgen.adb @@ -29,51 +29,124 @@ -- -- ------------------------------------------------------------------------------ --- The implementation here is portable to any IEEE implementation. It does --- not handle nonbinary radix, and also assumes that model numbers and --- machine numbers are basically identical, which is not true of all possible --- floating-point implementations. On a non-IEEE machine, this body must be --- specialized appropriately, or better still, its generic instantiations --- should be replaced by efficient machine-specific code. +-- This implementation is portable to any IEEE implementation. It does not +-- handle nonbinary radix, and also assumes that model numbers and machine +-- numbers are basically identical, which is not true of all possible +-- floating-point implementations. with Ada.Unchecked_Conversion; -with System; +with System.Unsigned_Types; use System.Unsigned_Types; -package body System.Fat_Gen is - - Float_Radix : constant T := T (T'Machine_Radix); - Radix_To_M_Minus_1 : constant T := Float_Radix ** (T'Machine_Mantissa - 1); +pragma Warnings (Off, "non-static constant in preelaborated unit"); +-- Every constant is static given our instantiation model +package body System.Fat_Gen is pragma Assert (T'Machine_Radix = 2); -- This version does not handle radix 16 - -- Constants for Decompose and Scaling + Rad : constant T := T (T'Machine_Radix); + -- Renaming for the machine radix - Rad : constant T := T (T'Machine_Radix); - Invrad : constant T := 1.0 / Rad; + Mantissa : constant Integer := T'Machine_Mantissa; + -- Renaming for the machine mantissa - subtype Expbits is Integer range 0 .. 6; - -- 2 ** (2 ** 7) might overflow. How big can radix-16 exponents get? - - Log_Power : constant array (Expbits) of Integer := (1, 2, 4, 8, 16, 32, 64); - - R_Power : constant array (Expbits) of T := - (Rad ** 1, - Rad ** 2, - Rad ** 4, - Rad ** 8, - Rad ** 16, - Rad ** 32, - Rad ** 64); - - R_Neg_Power : constant array (Expbits) of T := - (Invrad ** 1, - Invrad ** 2, - Invrad ** 4, - Invrad ** 8, - Invrad ** 16, - Invrad ** 32, - Invrad ** 64); + Invrad : constant T := 1.0 / Rad; + -- Smallest positive mantissa in the canonical form (RM A.5.3(4)) + + Small : constant T := Rad ** (T'Machine_Emin - 1); + pragma Unreferenced (Small); + -- Smallest positive normalized number + + Tiny : constant T := Rad ** (T'Machine_Emin - Mantissa); + -- Smallest positive denormalized number + + RM1 : constant T := Rad ** (Mantissa - 1); + -- Smallest positive member of the large consecutive integers. It is equal + -- to the ratio Small / Tiny, which means that multiplying by it normalizes + -- any nonzero denormalized number. + + IEEE_Emin : constant Integer := T'Machine_Emin - 1; + IEEE_Emax : constant Integer := T'Machine_Emax - 1; + -- The mantissa is a fraction with first digit set in Ada whereas it is + -- shifted by 1 digit to the left in the IEEE floating-point format. + + subtype IEEE_Erange is Integer range IEEE_Emin - 1 .. IEEE_Emax + 1; + -- The IEEE floating-point format extends the machine range by 1 to the + -- left for denormalized numbers and 1 to the right for infinities/NaNs. + + IEEE_Ebias : constant Integer := -(IEEE_Emin - 1); + -- The exponent is biased such that denormalized numbers have it zero + + -- The implementation uses a representation type Float_Rep that allows + -- direct access to exponent and mantissa of the floating point number. + + -- The Float_Rep type is a simple array of Float_Word elements. This + -- representation is chosen to make it possible to size the type based + -- on a generic parameter. Since the array size is known at compile + -- time, efficient code can still be generated. The size of Float_Word + -- elements should be large enough to allow accessing the exponent in + -- one read, but small enough so that all floating-point object sizes + -- are a multiple of Float_Word'Size. + + -- The following conditions must be met for all possible instantiations + -- of the attribute package: + + -- - T'Size is an integral multiple of Float_Word'Size + + -- - The exponent and sign are completely contained in a single + -- component of Float_Rep, named Most Significant Word (MSW). + + -- - The sign occupies the most significant bit of the MSW and the + -- exponent is in the following bits. The exception is 80-bit + -- double extended, where they occupy the low 16-bit halfword. + + -- The low-level primitives Copy_Sign, Decompose, Scaling and Valid are + -- implemented by accessing the bit pattern of the floating-point number. + -- Only the normalization of denormalized numbers, if any, and the gradual + -- underflow are left to the hardware, mainly because there is some leeway + -- for the hardware implementation in this area: for example, the MSB of + -- the mantissa, which is 1 for normalized numbers and 0 for denormalized + -- numbers, may or may not be stored by the hardware. + + Siz : constant := (if System.Word_Size > 32 then 32 else System.Word_Size); + type Float_Word is mod 2**Siz; + + N : constant Natural := (T'Size + Siz - 1) / Siz; + Rep_Last : constant Natural := Natural'Min (N - 1, (Mantissa + 16) / Siz); + -- Determine the number of Float_Words needed for representing the + -- entire floating-point value. Do not take into account excessive + -- padding, as occurs on IA-64 where 80 bits floats get padded to 128 + -- bits. In general, the exponent field cannot be larger than 15 bits, + -- even for 128-bit floating-point types, so the final format size + -- won't be larger than Mantissa + 16. + + type Float_Rep is array (Natural range 0 .. N - 1) of Float_Word; + pragma Suppress_Initialization (Float_Rep); + -- This pragma suppresses the generation of an initialization procedure + -- for type Float_Rep when operating in Initialize/Normalize_Scalars mode. + + MSW : constant Natural := Rep_Last * Standard'Default_Bit_Order; + -- Finding the location of the Exponent_Word is a bit tricky. In general + -- we assume Word_Order = Bit_Order. + + Exp_Factor : constant Float_Word := + (if Mantissa = 64 + then 1 + else 2**(Siz - 1) / Float_Word (IEEE_Emax - IEEE_Emin + 3)); + -- Factor that the extracted exponent needs to be divided by to be in + -- range 0 .. IEEE_Emax - IEEE_Emin + 2. The special case is 80-bit + -- double extended, where the exponent starts the 3rd float word. + + Exp_Mask : constant Float_Word := + Float_Word (IEEE_Emax - IEEE_Emin + 2) * Exp_Factor; + -- Value needed to mask out the exponent field. This assumes that the + -- range 0 .. IEEE_Emax - IEEE_Emin + 2 contains 2**N values, for some + -- N in Natural. + + Sign_Mask : constant Float_Word := + (if Mantissa = 64 then 2**15 else 2**(Siz - 1)); + -- Value needed to mask out the sign field. The special case is 80-bit + -- double extended, where the exponent starts the 3rd float word. ----------------------- -- Local Subprograms -- @@ -85,11 +158,6 @@ package body System.Fat_Gen is -- the sign of the exponent. The absolute value of Frac is in the range -- 0.0 <= Frac < 1.0. If Frac = 0.0 or -0.0, then Expo is always zero. - function Gradual_Scaling (Adjustment : UI) return T; - -- Like Scaling with a first argument of 1.0, but returns the smallest - -- denormal rather than zero when the adjustment is smaller than - -- Machine_Emin. Used for Succ and Pred. - -------------- -- Adjacent -- -------------- @@ -139,19 +207,22 @@ package body System.Fat_Gen is --------------- function Copy_Sign (Value, Sign : T) return T is - Result : T; + S : constant T := T'Machine (Sign); - function Is_Negative (V : T) return Boolean; - pragma Import (Intrinsic, Is_Negative); + Rep_S : Float_Rep; + for Rep_S'Address use S'Address; + -- Rep_S is a view of the Sign parameter - begin - Result := abs Value; + V : T := T'Machine (Value); - if Is_Negative (Sign) then - return -Result; - else - return Result; - end if; + Rep_V : Float_Rep; + for Rep_V'Address use V'Address; + -- Rep_V is a view of the Value parameter + + begin + Rep_V (MSW) := + (Rep_V (MSW) and not Sign_Mask) or (Rep_S (MSW) and Sign_Mask); + return V; end Copy_Sign; --------------- @@ -159,94 +230,53 @@ package body System.Fat_Gen is --------------- procedure Decompose (XX : T; Frac : out T; Expo : out UI) is - X : constant T := T'Machine (XX); - - begin - if X = 0.0 then - - -- The normalized exponent of zero is zero, see RM A.5.2(15) + X : T := T'Machine (XX); - Frac := X; - Expo := 0; - - -- Check for infinities, transfinites, whatnot + Rep : Float_Rep; + for Rep'Address use X'Address; + -- Rep is a view of the input floating-point parameter - elsif X > T'Safe_Last then - Frac := Invrad; - pragma Annotate (CodePeer, Intentional, "dead code", - "Check float range."); - Expo := T'Machine_Emax + 1; + Exp : constant IEEE_Erange := + Integer ((Rep (MSW) and Exp_Mask) / Exp_Factor) - IEEE_Ebias; + -- Mask/Shift X to only get bits from the exponent. Then convert biased + -- value to final value. - elsif X < T'Safe_First then - Frac := -Invrad; - pragma Annotate (CodePeer, Intentional, "dead code", - "Check float range."); - Expo := T'Machine_Emax + 2; -- how many extra negative values? + Minus : constant Boolean := (Rep (MSW) and Sign_Mask) /= 0; + -- Mask/Shift X to only get bit from the sign - else - -- Case of nonzero finite x. Essentially, we just multiply - -- by Rad ** (+-2**N) to reduce the range. + begin + -- The normalized exponent of zero is zero, see RM A.5.3(15) - declare - Ax : T := abs X; - Ex : UI := 0; + if X = 0.0 then + Expo := 0; + Frac := X; - -- Ax * Rad ** Ex is invariant + -- Check for infinities and NaNs - begin - if Ax >= 1.0 then - while Ax >= R_Power (Expbits'Last) loop - Ax := Ax * R_Neg_Power (Expbits'Last); - Ex := Ex + Log_Power (Expbits'Last); - end loop; + elsif Exp = IEEE_Emax + 1 then + Expo := T'Machine_Emax + 1; + Frac := (if Minus then -Invrad else Invrad); - -- Ax < Rad ** 64 + -- Check for nonzero denormalized numbers - for N in reverse Expbits'First .. Expbits'Last - 1 loop - if Ax >= R_Power (N) then - Ax := Ax * R_Neg_Power (N); - Ex := Ex + Log_Power (N); - end if; + elsif Exp = IEEE_Emin - 1 then + -- Normalize by multiplying by Radix ** (Mantissa - 1) - -- Ax < R_Power (N) + Decompose (X * RM1, Frac, Expo); + Expo := Expo - (Mantissa - 1); - end loop; + -- Case of normalized numbers - -- 1 <= Ax < Rad + else + -- The Ada exponent is the IEEE exponent plus 1, see above - Ax := Ax * Invrad; - Ex := Ex + 1; + Expo := Exp + 1; - else - -- 0 < ax < 1 - - while Ax < R_Neg_Power (Expbits'Last) loop - Ax := Ax * R_Power (Expbits'Last); - pragma Annotate (CodePeer, Intentional, "dead code", - "Check float range."); - Ex := Ex - Log_Power (Expbits'Last); - end loop; - pragma Annotate - (CodePeer, Intentional, - "test always false", - "expected for some instantiations"); - - -- Rad ** -64 <= Ax < 1 - - for N in reverse Expbits'First .. Expbits'Last - 1 loop - if Ax < R_Neg_Power (N) then - Ax := Ax * R_Power (N); - Ex := Ex - Log_Power (N); - end if; - - -- R_Neg_Power (N) <= Ax < 1 - - end loop; - end if; + -- Set Ada exponent of X to zero, so we end up with the fraction - Frac := (if X > 0.0 then Ax else -Ax); - Expo := Ex; - end; + Rep (MSW) := (Rep (MSW) and not Exp_Mask) + + Float_Word (IEEE_Ebias - 1) * Exp_Factor; + Frac := X; end if; end Decompose; @@ -292,38 +322,6 @@ package body System.Fat_Gen is return X_Frac; end Fraction; - --------------------- - -- Gradual_Scaling -- - --------------------- - - function Gradual_Scaling (Adjustment : UI) return T is - Y : T; - Y1 : T; - Ex : UI := Adjustment; - - begin - if Adjustment < T'Machine_Emin - 1 then - Y := 2.0 ** T'Machine_Emin; - Y1 := Y; - Ex := Ex - T'Machine_Emin; - while Ex < 0 loop - Y := T'Machine (Y / 2.0); - - if Y = 0.0 then - return Y1; - end if; - - Ex := Ex + 1; - Y1 := Y; - end loop; - - return Y1; - - else - return Scaling (1.0, Adjustment); - end if; - end Gradual_Scaling; - ------------------ -- Leading_Part -- ------------------ @@ -333,7 +331,7 @@ package body System.Fat_Gen is Y, Z : T; begin - if Radix_Digits >= T'Machine_Mantissa then + if Radix_Digits >= Mantissa then return X; elsif Radix_Digits <= 0 then @@ -420,12 +418,11 @@ package body System.Fat_Gen is -- Zero has to be treated specially, since its exponent is zero if X = 0.0 then - return -Succ (X); + return -Tiny; - -- Special treatment for most negative number + -- Special treatment for largest negative number: raise Constraint_Error elsif X = T'First then - raise Constraint_Error with "Pred of largest negative number"; -- For infinities, return unchanged @@ -439,28 +436,33 @@ package body System.Fat_Gen is -- Subtract from the given number a number equivalent to the value -- of its least significant bit. Given that the most significant bit - -- represents a value of 1.0 * radix ** (exp - 1), the value we want - -- is obtained by shifting this by (mantissa-1) bits to the right, + -- represents a value of 1.0 * Radix ** (Exp - 1), the value we want + -- is obtained by shifting this by (Mantissa-1) bits to the right, -- i.e. decreasing the exponent by that amount. else Decompose (X, X_Frac, X_Exp); - -- A special case, if the number we had was a positive power of - -- two, then we want to subtract half of what we would otherwise - -- subtract, since the exponent is going to be reduced. + -- For a denormalized number or a normalized number with the lowest + -- exponent, just subtract the Tiny. + + if X_Exp <= T'Machine_Emin then + return X - Tiny; - -- Note that X_Frac has the same sign as X, so if X_Frac is 0.5, - -- then we know that we have a positive number (and hence a - -- positive power of 2). + -- A special case, if the number we had was a power of two on the + -- positive side of zero, then we want to subtract half of what we + -- would have subtracted, since the exponent is going to be reduced. - if X_Frac = 0.5 then - return X - Gradual_Scaling (X_Exp - T'Machine_Mantissa - 1); + -- Note that X_Frac has the same sign as X so, if X_Frac is Invrad, + -- then we know that we had a power of two on the positive side. - -- Otherwise the exponent is unchanged + elsif X_Frac = Invrad then + return X - Scaling (1.0, X_Exp - Mantissa - 1); + + -- Otherwise the adjustment is unchanged else - return X - Gradual_Scaling (X_Exp - T'Machine_Mantissa); + return X - Scaling (1.0, X_Exp - Mantissa); end if; end if; end Pred; @@ -580,70 +582,90 @@ package body System.Fat_Gen is -- Scaling -- ------------- - -- Return x * rad ** adjustment quickly, or quietly underflow to zero, - -- or overflow naturally. - function Scaling (X : T; Adjustment : UI) return T is + pragma Assert (Mantissa <= 64); + -- This implementation handles only 80-bit IEEE Extended or smaller + + XX : T := T'Machine (X); + + Rep : Float_Rep; + for Rep'Address use XX'Address; + -- Rep is a view of the input floating-point parameter + + Exp : constant IEEE_Erange := + Integer ((Rep (MSW) and Exp_Mask) / Exp_Factor) - IEEE_Ebias; + -- Mask/Shift X to only get bits from the exponent. Then convert biased + -- value to final value. + + Minus : constant Boolean := (Rep (MSW) and Sign_Mask) /= 0; + -- Mask/Shift X to only get bit from the sign + + Expi, Expf : IEEE_Erange; + begin - if X = 0.0 or else Adjustment = 0 then + -- Check for zero, infinities, NaNs as well as no adjustment + + if X = 0.0 or else Exp = IEEE_Emax + 1 or else Adjustment = 0 then return X; - end if; - -- Nonzero x essentially, just multiply repeatedly by Rad ** (+-2**n) + -- Check for nonzero denormalized numbers - declare - Y : T := X; - Ex : UI := Adjustment; + elsif Exp = IEEE_Emin - 1 then + -- Check for zero result to protect the subtraction below - -- Y * Rad ** Ex is invariant + if Adjustment < -(Mantissa - 1) then + XX := 0.0; + return (if Minus then -XX else XX); - begin - if Ex < 0 then - while Ex <= -Log_Power (Expbits'Last) loop - Y := Y * R_Neg_Power (Expbits'Last); - Ex := Ex + Log_Power (Expbits'Last); - end loop; + -- Normalize by multiplying by Radix ** (Mantissa - 1) - -- -64 < Ex <= 0 + else + return Scaling (XX * RM1, Adjustment - (Mantissa - 1)); + end if; - for N in reverse Expbits'First .. Expbits'Last - 1 loop - if Ex <= -Log_Power (N) then - Y := Y * R_Neg_Power (N); - Ex := Ex + Log_Power (N); - end if; + -- Case of normalized numbers - -- -Log_Power (N) < Ex <= 0 + else + -- Check for overflow - end loop; + if Adjustment > IEEE_Emax - Exp then + XX := 0.0; + return (if Minus then -1.0 / XX else 1.0 / XX); - -- Ex = 0 + -- Check for underflow - else - -- Ex >= 0 + elsif Adjustment < IEEE_Emin - Exp then + -- Check for gradual underflow - while Ex >= Log_Power (Expbits'Last) loop - Y := Y * R_Power (Expbits'Last); - Ex := Ex - Log_Power (Expbits'Last); - end loop; + if T'Denorm + and then Adjustment >= IEEE_Emin - (Mantissa - 1) - Exp + then + Expf := IEEE_Emin; + Expi := Exp + Adjustment - Expf; - -- 0 <= Ex < 64 + -- Case of zero result - for N in reverse Expbits'First .. Expbits'Last - 1 loop - if Ex >= Log_Power (N) then - Y := Y * R_Power (N); - Ex := Ex - Log_Power (N); - end if; + else + XX := 0.0; + return (if Minus then -XX else XX); + end if; - -- 0 <= Ex < Log_Power (N) + -- Case of normalized results - end loop; + else + Expf := Exp + Adjustment; + Expi := 0; + end if; - -- Ex = 0 + Rep (MSW) := (Rep (MSW) and not Exp_Mask) + + Float_Word (IEEE_Ebias + Expf) * Exp_Factor; + if Expi < 0 then + XX := XX / T (Long_Long_Unsigned (2) ** (-Expi)); end if; - return Y; - end; + return XX; + end if; end Scaling; ---------- @@ -653,34 +675,18 @@ package body System.Fat_Gen is function Succ (X : T) return T is X_Frac : T; X_Exp : UI; - X1, X2 : T; begin -- Treat zero specially since it has a zero exponent if X = 0.0 then - X1 := 2.0 ** T'Machine_Emin; + return Tiny; - -- Following loop generates smallest denormal - - loop - X2 := T'Machine (X1 / 2.0); - exit when X2 = 0.0; - X1 := X2; - end loop; - - return X1; - - -- Special treatment for largest positive number + -- Special treatment for largest positive number: raise Constraint_Error elsif X = T'Last then - - -- If not generating infinities, we raise a constraint error - raise Constraint_Error with "Succ of largest positive number"; - -- Otherwise generate a positive infinity - -- For infinities, return unchanged elsif X < T'First or else X > T'Last then @@ -690,30 +696,35 @@ package body System.Fat_Gen is pragma Annotate (CodePeer, Intentional, "dead code", "Check float range."); - -- Add to the given number a number equivalent to the value - -- of its least significant bit. Given that the most significant bit - -- represents a value of 1.0 * radix ** (exp - 1), the value we want - -- is obtained by shifting this by (mantissa-1) bits to the right, + -- Add to the given number a number equivalent to the value of its + -- least significant bit. Given that the most significant bit + -- represents a value of 1.0 * Radix ** (Exp - 1), the value we want + -- is obtained by shifting this by (Mantissa-1) bits to the right, -- i.e. decreasing the exponent by that amount. else Decompose (X, X_Frac, X_Exp); - -- A special case, if the number we had was a negative power of two, - -- then we want to add half of what we would otherwise add, since the - -- exponent is going to be reduced. + -- For a denormalized number or a normalized number with the lowest + -- exponent, just add the Tiny. + + if X_Exp <= T'Machine_Emin then + return X + Tiny; - -- Note that X_Frac has the same sign as X, so if X_Frac is -0.5, - -- then we know that we have a negative number (and hence a negative - -- power of 2). + -- A special case, if the number we had was a power of two on the + -- negative side of zero, then we want to add half of what we would + -- have added, since the exponent is going to be reduced. - if X_Frac = -0.5 then - return X + Gradual_Scaling (X_Exp - T'Machine_Mantissa - 1); + -- Note that X_Frac has the same sign as X, so if X_Frac is -Invrad, + -- then we know that we had a power of two on the negative side. - -- Otherwise the exponent is unchanged + elsif X_Frac = -Invrad then + return X + Scaling (1.0, X_Exp - Mantissa - 1); + + -- Otherwise the adjustment is unchanged else - return X + Gradual_Scaling (X_Exp - T'Machine_Mantissa); + return X + Scaling (1.0, X_Exp - Mantissa); end if; end if; end Succ; @@ -726,7 +737,7 @@ package body System.Fat_Gen is -- T'Machine (RM1 + N) - RM1 - -- where N >= 0.0 and RM1 = radix ** (mantissa - 1) + -- where N >= 0.0 and RM1 = Radix ** (Mantissa - 1) -- This works provided that the intermediate result (RM1 + N) does not -- have extra precision (which is why we call Machine). When we compute @@ -743,19 +754,18 @@ package body System.Fat_Gen is begin Result := abs X; - if Result >= Radix_To_M_Minus_1 then + if Result >= RM1 then return T'Machine (X); else - Result := - T'Machine (Radix_To_M_Minus_1 + Result) - Radix_To_M_Minus_1; + Result := T'Machine (RM1 + Result) - RM1; if Result > abs X then Result := Result - 1.0; end if; if X > 0.0 then - return Result; + return Result; elsif X < 0.0 then return -Result; @@ -806,86 +816,11 @@ package body System.Fat_Gen is ----------- function Valid (X : not null access T) return Boolean is - IEEE_Emin : constant Integer := T'Machine_Emin - 1; - IEEE_Emax : constant Integer := T'Machine_Emax - 1; - -- The mantissa is a fraction with first digit set in Ada whereas it is - -- shifted by 1 digit to the left in the IEEE floating-point format. - - subtype IEEE_Erange is Integer range IEEE_Emin - 1 .. IEEE_Emax + 1; - -- The IEEE floating-point format extends the machine range by 1 to the - -- left for denormalized numbers and 1 to the right for infinities/NaNs. - - IEEE_Ebias : constant Integer := -(IEEE_Emin - 1); - -- The exponent is biased such that denormalized numbers have it zero - - -- The implementation uses a representation type Float_Rep that allows - -- direct access to exponent and mantissa of the floating point number. - - -- The Float_Rep type is a simple array of Float_Word elements. This - -- representation is chosen to make it possible to size the type based - -- on a generic parameter. Since the array size is known at compile - -- time, efficient code can still be generated. The size of Float_Word - -- elements should be large enough to allow accessing the exponent in - -- one read, but small enough so that all floating-point object sizes - -- are a multiple of Float_Word'Size. - - -- The following conditions must be met for all possible instantiations - -- of the attribute package: - - -- - T'Size is an integral multiple of Float_Word'Size - - -- - The exponent and sign are completely contained in a single - -- component of Float_Rep, named Most Significant Word (MSW). - - -- - The sign occupies the most significant bit of the MSW and the - -- exponent is in the following bits. The exception is 80-bit - -- double extended, where they occupy the low 16-bit halfword. - - Siz : constant := - (if System.Word_Size > 32 then 32 else System.Word_Size); - type Float_Word is mod 2**Siz; - - N : constant Natural := (T'Size + Siz - 1) / Siz; - Rep_Last : constant Natural := - Natural'Min (N - 1, (T'Machine_Mantissa + 16) / Siz); - -- Determine the number of Float_Words needed for representing the - -- entire floating-point value. Do not take into account excessive - -- padding, as occurs on IA-64 where 80 bits floats get padded to 128 - -- bits. In general, the exponent field cannot be larger than 15 bits, - -- even for 128-bit floating-point types, so the final format size - -- won't be larger than T'Machine_Mantissa + 16. - - type Float_Rep is array (Natural range 0 .. N - 1) of Float_Word; - pragma Suppress_Initialization (Float_Rep); - -- This pragma suppresses the generation of an initialization procedure - -- for type Float_Rep when operating in Initialize/Normalize_Scalars - -- mode, which would be annoying since Valid has got a pragma Inline. - - MSW : constant Natural := Rep_Last * Standard'Default_Bit_Order; - -- Finding the location of the Exponent_Word is a bit tricky. In general - -- we assume Word_Order = Bit_Order. - - Exp_Factor : constant Float_Word := - (if T'Machine_Mantissa = 64 - then 1 - else 2**(Siz - 1) / - Float_Word (IEEE_Emax - IEEE_Emin + 3)); - -- Factor that the extracted exponent needs to be divided by to be in - -- range 0 .. IEEE_Emax - IEEE_Emin + 2. The special case is 80-bit - -- double extended, where the exponent starts the 3rd float word. - - Exp_Mask : constant Float_Word := - Float_Word (IEEE_Emax - IEEE_Emin + 2) * Exp_Factor; - -- Value needed to mask out the exponent field. This assumes that the - -- range 0 .. IEEE_Emax - IEEE_Emin + 2 contains 2**N values, for some - -- N in Natural. - type Access_T is access all T; function To_Address is new Ada.Unchecked_Conversion (Access_T, System.Address); Rep : Float_Rep; - pragma Import (Ada, Rep); for Rep'Address use To_Address (Access_T (X)); -- Rep is a view of the input floating-point parameter. Note that we -- must avoid reading the actual bits of this parameter in float form diff --git a/gcc/ada/libgnat/s-fatgen.ads b/gcc/ada/libgnat/s-fatgen.ads index b8bdf2d2..700cfdc 100644 --- a/gcc/ada/libgnat/s-fatgen.ads +++ b/gcc/ada/libgnat/s-fatgen.ads @@ -31,9 +31,8 @@ -- This generic package provides a target independent implementation of the -- floating-point attributes that denote functions. The implementations here --- are portable, but very slow. The runtime contains a set of instantiations --- of this package for all predefined floating-point types, and these should --- be replaced by efficient assembly language code where possible. +-- should be portable and reasonably efficient. The runtime contains a set of +-- instantiations of this package for all predefined floating-point types. generic type T is digits <>; @@ -107,6 +106,10 @@ package System.Fat_Gen is -- floating point register). private + pragma Inline (Compose); + pragma Inline (Copy_Sign); + pragma Inline (Exponent); + pragma Inline (Fraction); pragma Inline (Machine); pragma Inline (Model); pragma Inline (Valid); |