* [Ada] Ada.Numerics.Big_Numbers.Big_Reals.To_Big_Real looses precision
@ 2020-11-26 8:41 Pierre-Marie de Rodat
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From: Pierre-Marie de Rodat @ 2020-11-26 8:41 UTC (permalink / raw)
To: gcc-patches; +Cc: Arnaud Charlet
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The initial implementation was simply using 'Image which will loose
precision in some cases. Fixed by always using a sufficient number of
digits.
To_Big_Real could be made more efficient by not going through strings,
this is left for a later step.
Tested on x86_64-pc-linux-gnu, committed on trunk
gcc/ada/
* libgnat/a-nbnbre.adb (To_Big_Real): Do not loose precision.
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diff --git a/gcc/ada/libgnat/a-nbnbre.adb b/gcc/ada/libgnat/a-nbnbre.adb
--- a/gcc/ada/libgnat/a-nbnbre.adb
+++ b/gcc/ada/libgnat/a-nbnbre.adb
@@ -32,6 +32,7 @@
-- This is the default version of this package, based on Big_Integers only.
with Ada.Strings.Text_Output.Utils;
+with System.Img_Real; use System.Img_Real;
package body Ada.Numerics.Big_Numbers.Big_Reals is
@@ -122,8 +123,15 @@ package body Ada.Numerics.Big_Numbers.Big_Reals is
-----------------
function To_Big_Real (Arg : Num) return Valid_Big_Real is
+ S : String (1 .. Max_Real_Image_Length);
+ P : Natural := 0;
begin
- return From_String (Arg'Image);
+ -- Use Long_Long_Unsigned'Width - 1 digits = 20 which is sufficient
+ -- for the largest floating point format.
+
+ Set_Image_Real
+ (Long_Long_Float (Arg), S, P, Fore => 1, Aft => 20, Exp => 5);
+ return From_String (S (1 .. P));
end To_Big_Real;
-------------------
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2020-11-26 8:41 [Ada] Ada.Numerics.Big_Numbers.Big_Reals.To_Big_Real looses precision Pierre-Marie de Rodat
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