fix int promotion for >8-bit stdint.h types

Author: Vexu

src/helpers.zig

@@ -203,6 +203,16 @@ test "ArithmeticConversion" {
     try Test.checkPromotion(c_uint, c_long, c_long);
 
     try Test.checkPromotion(c_ulong, c_longlong, c_ulonglong);
+
+    // stdint.h
+    try Test.checkPromotion(u8, i8, c_int);
+    try Test.checkPromotion(u16, i16, c_int);
+    try Test.checkPromotion(i32, c_int, c_int);
+    try Test.checkPromotion(u32, c_int, c_uint);
+    try Test.checkPromotion(i64, c_int, c_long);
+    try Test.checkPromotion(u64, c_int, c_ulong);
+    try Test.checkPromotion(isize, c_int, c_long);
+    try Test.checkPromotion(usize, c_int, c_ulong);
 }
 
 const F_SUFFIX = @import("helpers/F_SUFFIX.zig").F_SUFFIX;

src/helpers/arithmetic_conversion.zig

@@ -35,15 +35,24 @@ pub fn ArithmeticConversion(comptime A: type, comptime B: type) type {
 /// Integer promotion described in C11 6.3.1.1.2
 fn PromotedIntType(comptime T: type) type {
     return switch (T) {
-        bool, u8, i8, c_short => c_int,
+        bool, c_short => c_int,
         c_ushort => if (@sizeOf(c_ushort) == @sizeOf(c_int)) c_uint else c_int,
         c_int, c_uint, c_long, c_ulong, c_longlong, c_ulonglong => T,
-        else => if (T == comptime_int) {
-            @compileError("Cannot promote `" ++ @typeName(T) ++ "`; a fixed-size number type is required");
-        } else if (@typeInfo(T) == .int) {
-            @compileError("Cannot promote `" ++ @typeName(T) ++ "`; a C ABI type is required");
-        } else {
-            @compileError("Attempted to promote invalid type `" ++ @typeName(T) ++ "`");
+        else => switch (@typeInfo(T)) {
+            .comptime_int => @compileError("Cannot promote `" ++ @typeName(T) ++ "`; a fixed-size number type is required"),
+            // promote to c_int if it can represent all values of T
+            .int => |int_info| if (int_info.bits < @bitSizeOf(c_int))
+                c_int
+                // otherwise, restore the original C type
+            else if (int_info.bits == @bitSizeOf(c_int))
+                if (int_info.signedness == .unsigned) c_uint else c_int
+            else if (int_info.bits <= @bitSizeOf(c_long))
+                if (int_info.signedness == .unsigned) c_ulong else c_long
+            else if (int_info.bits <= @bitSizeOf(c_longlong))
+                if (int_info.signedness == .unsigned) c_ulonglong else c_longlong
+            else
+                @compileError("Cannot promote `" ++ @typeName(T) ++ "`; a C ABI type is required"),
+            else => @compileError("Attempted to promote invalid type `" ++ @typeName(T) ++ "`"),
         },
     };
 }

test/macros.zig

@@ -130,6 +130,7 @@ test "Macro that uses division operator" {
             true,
         ),
     );
+
     try expectEqual(
         @as(c_int, 21),
         macros.DIVIDE_ARGS(
@@ -138,6 +139,14 @@ test "Macro that uses division operator" {
         ),
     );
 
+    try expectEqual(
+        @as(c_uint, 21),
+        macros.DIVIDE_ARGS(
+            @as(u32, 42),
+            @as(u32, 2),
+        ),
+    );
+
     try expectEqual(
         @as(c_int, 21),
         macros.DIVIDE_ARGS(