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[Ada] Fix computation of Prec/Succ of zero without denormals

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gcc/ada/

	* libgnat/s-fatgen.adb: Add use clause for Interfaces.Unsigned_16
	and Interfaces.Unsigned_32.
	(Small16): New constant.
	(Small32): Likewise.
	(Small64): Likewise.
	(Small80): Likewise.
	(Pred): Declare a local overlay for Small and return it negated
	for zero if the type does not support denormalized numbers.
	(Succ): Likewise, but return it directly.
This commit is contained in:
Eric Botcazou 2020-12-10 21:02:07 +01:00 committed by Pierre-Marie de Rodat
parent 33d1be8739
commit 4e60fea920
1 changed files with 31 additions and 2 deletions
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33
gcc/ada/libgnat/s-fatgen.adb
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@ -42,6 +42,8 @@ pragma Warnings (Off, "non-static constant in preelaborated unit");
-- Every constant is static given our instantiation model
package body System.Fat_Gen is
use type Interfaces.Unsigned_16;
use type Interfaces.Unsigned_32;
use type Interfaces.Unsigned_64;
pragma Assert (T'Machine_Radix = 2);
@ -59,6 +61,18 @@ package body System.Fat_Gen is
-- Small : constant T := Rad ** (T'Machine_Emin - 1);
-- Smallest positive normalized number
Small16 : constant Interfaces.Unsigned_16 := 2**(Mantissa - 1);
Small32 : constant Interfaces.Unsigned_32 := 2**(Mantissa - 1);
Small64 : constant Interfaces.Unsigned_64 := 2**(Mantissa - 1);
Small80 : constant array (1 .. 2) of Interfaces.Unsigned_64 :=
(2**48 * (1 - Standard'Default_Bit_Order),
1 * Standard'Default_Bit_Order);
for Small80'Alignment use Standard'Maximum_Alignment;
-- We cannot use the direct declaration because it cannot be translated
-- into C90, as the hexadecimal floating constants were introduced in C99.
-- So we work around this by using an overlay of the integer constant.
-- ??? Revisit this when the new CCG technoloy is in production
-- Tiny : constant T := Rad ** (T'Machine_Emin - Mantissa);
-- Smallest positive denormalized number
@ -72,6 +86,7 @@ package body System.Fat_Gen is
-- We cannot use the direct declaration because it cannot be translated
-- into C90, as the hexadecimal floating constants were introduced in C99.
-- So we work around this by using an overlay of the integer constant.
-- ??? Revisit this when the new CCG technoloy is in production
RM1 : constant T := Rad ** (Mantissa - 1);
-- Smallest positive member of the large consecutive integers. It is equal
@ -424,6 +439,13 @@ package body System.Fat_Gen is
----------
function Pred (X : T) return T is
Small : constant T;
pragma Import (Ada, Small);
for Small'Address use (if T'Size = 16 then Small16'Address
elsif T'Size = 32 then Small32'Address
elsif T'Size = 64 then Small64'Address
elsif Mantissa = 64 then Small80'Address
else raise Program_Error);
Tiny : constant T;
pragma Import (Ada, Tiny);
for Tiny'Address use (if T'Size = 16 then Tiny16'Address
@ -438,7 +460,7 @@ package body System.Fat_Gen is
-- Zero has to be treated specially, since its exponent is zero
if X = 0.0 then
return -Tiny;
return -(if T'Denorm then Tiny else Small);
-- Special treatment for largest negative number: raise Constraint_Error
@ -700,6 +722,13 @@ package body System.Fat_Gen is
----------
function Succ (X : T) return T is
Small : constant T;
pragma Import (Ada, Small);
for Small'Address use (if T'Size = 16 then Small16'Address
elsif T'Size = 32 then Small32'Address
elsif T'Size = 64 then Small64'Address
elsif Mantissa = 64 then Small80'Address
else raise Program_Error);
Tiny : constant T;
pragma Import (Ada, Tiny);
for Tiny'Address use (if T'Size = 16 then Tiny16'Address
@ -714,7 +743,7 @@ package body System.Fat_Gen is
-- Treat zero specially since it has a zero exponent
if X = 0.0 then
return Tiny;
return (if T'Denorm then Tiny else Small);
-- Special treatment for largest positive number: raise Constraint_Error