[m-rev.] diff: large integer literals in java backend

[Peter Wang]

Other suggestions welcome.


Branches: main

When using a 64-bit Mercury compiler, a hexadecimal literal with the 32nd bit
set (e.g. 0xffffffff) would be written out to Java source files as a large
positive integer, but the Java compiler would complain because the integer is
too large to fit in 32-bits.

This patch works around the problem by writing such literals in hexadecimal.

compiler/mlds_to_java.m:
        As above.

diff --git a/compiler/mlds_to_java.m b/compiler/mlds_to_java.m
index 9b43902..7fddc3b 100644
--- a/compiler/mlds_to_java.m
+++ b/compiler/mlds_to_java.m
@@ -3663,7 +3663,7 @@ output_rval_const(Const, !IO) :-
         io.write_string("false", !IO)
     ;
         Const = mlconst_int(N),
-        io.write_int(N, !IO)
+        output_int_const(N, !IO)
     ;
         Const = mlconst_foreign(Lang, Value, _Type),
         expect(unify(Lang, lang_java), this_file,
@@ -3699,6 +3699,28 @@ output_rval_const(Const, !IO) :-
         io.write_string(Initializer, !IO)
     ).

+:- pred output_int_const(int::in, io::di, io::uo) is det.
+
+output_int_const(N, !IO) :-
+    % The Mercury compiler could be using 64-bit integers but Java has 32-bit
+    % ints.  A literal 0xffffffff in a source file would be interpreted by a
+    % 64-bit Mercury compiler as 4294967295.  If it is written out in decimal a
+    % Java compiler would rightly complain because the integer is too large to
+    % fit in a 32-bit int.  However, it won't complain if the literal is
+    % expressed in hexadecimal (nor as the negative decimal -1).
+    ( N < 0 ->
+        io.write_int(N, !IO)
+    ;
+        N >> 32 = 0,
+        N /\ 0x80000000 = 0x80000000
+    ->
+        % The bit pattern fits in 32 bits, but is too large to write as a
+        % positive decimal.  This branch is unreachable on a 32-bit compiler.
+        io.format("0x%x", [i(N /\ 0xffffffff)], !IO)
+    ;
+        io.write_int(N, !IO)
+    ).
+
 %-----------------------------------------------------------------------------%

 :- pred mlds_output_code_addr(mlds_code_addr::in, bool::in, io::di,
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