While the default function returning 128-bit integer works correctly,
Random_Discrete does not if it is instantiated on a 128-bit integer,
since the magnitude of the returned numbers is still 64 bits.
Note that no counterpart is needed in GNAT.Random_Numbers because the
homonymous function in there is just a forwarder for the original one.
Tested on x86_64-pc-linux-gnu, committed on trunk
gcc/ada/
* libgnat/s-rannum.adb (Random_Discrete): Specifically deal with
the case where the size of the base type is larger than 64 bits.diff --git a/gcc/ada/libgnat/s-rannum.adb b/gcc/ada/libgnat/s-rannum.adb
--- a/gcc/ada/libgnat/s-rannum.adb
+++ b/gcc/ada/libgnat/s-rannum.adb
@@ -409,6 +409,41 @@ is
elsif Max < Min then
raise Constraint_Error;
+ -- In the 128-bit case, we have to be careful since not all 128-bit
+ -- unsigned values are representable in GNAT's universal integer.
+
+ elsif Result_Subtype'Base'Size > 64 then
+ declare
+ -- Ignore unequal-size warnings since GNAT's handling is correct.
+
+ pragma Warnings ("Z");
+ function Conv_To_Unsigned is
+ new Unchecked_Conversion (Result_Subtype'Base, Unsigned_128);
+ function Conv_To_Result is
+ new Unchecked_Conversion (Unsigned_128, Result_Subtype'Base);
+ pragma Warnings ("z");
+
+ N : constant Unsigned_128 :=
+ Conv_To_Unsigned (Max) - Conv_To_Unsigned (Min) + 1;
+
+ X, Slop : Unsigned_128;
+
+ begin
+ if N = 0 then
+ return Conv_To_Result (Conv_To_Unsigned (Min) + Random (Gen));
+
+ else
+ Slop := Unsigned_128'Last rem N + 1;
+
+ loop
+ X := Random (Gen);
+ exit when Slop = N or else X <= Unsigned_128'Last - Slop;
+ end loop;
+
+ return Conv_To_Result (Conv_To_Unsigned (Min) + X rem N);
+ end if;
+ end;
+
-- In the 64-bit case, we have to be careful since not all 64-bit
-- unsigned values are representable in GNAT's universal integer.
