C backend: better f128 support

src/codegen/c.zig

@@ -154,6 +154,7 @@ const reserved_idents = std.ComptimeStringMap(void, .{
     .{ "enum", {} },
     .{ "extern ", {} },
     .{ "float", {} },
+    .{ "float128_t", {} },
     .{ "for", {} },
     .{ "fortran", {} },
     .{ "goto", {} },
@@ -420,6 +421,7 @@ pub const DeclGen = struct {
         const int_info = @typeInfo(@TypeOf(int_val)).Int;
         const is_signed = int_info.signedness == .signed;
         const is_neg = int_val < 0;
+
         comptime assert(int_info.bits > 64 and int_info.bits <= 128);
 
         // TODO support big endian arch
@@ -433,13 +435,27 @@ pub const DeclGen = struct {
         const low = @truncate(u64, magnitude);
 
         // (int128_t)/<->( ( (uint128_t)( val_high << 64 )u ) + (uint128_t)val_low/u )
-        if (is_signed) try writer.writeAll("(int128_t)");
-        if (is_neg) try writer.writeByte('-');
+        if (is_signed) {
+            try writer.writeAll("(int128_t)");
+            if (is_neg)
+                try writer.writeByte('-');
+        } else {
+            try writer.writeAll("(uint128_t)");
+        }
+
+        if (magnitude == 0)
+            return writer.print("0", .{});
 
-        try writer.print("(((uint128_t)0x{x}u<<64)", .{high});
+        try writer.print("(", .{});
+
+        if (high > 0)
+            try writer.print("((uint128_t)0x{x}u << 64)", .{high});
+
+        if (high > 0 and low > 0)
+            try writer.print(" + ", .{});
 
         if (low > 0)
-            try writer.print("+(uint128_t)0x{x}u", .{low});
+            try writer.print("(uint128_t)0x{x}u", .{low});
 
         return writer.writeByte(')');
     }
@@ -539,6 +555,35 @@ pub const DeclGen = struct {
         }
     }
 
+    fn renderSmallFloat(
+        dg: *DeclGen,
+        comptime T: type,
+        writer: anytype,
+        val: Value,
+    ) error{ OutOfMemory, AnalysisFail }!void {
+        const v = val.toFloat(T);
+        if (std.math.isNan(v) or std.math.isInf(v)) {
+            // just generate a bit cast (exactly like we do in airBitcast)
+            switch (T) {
+                f16 => return dg.fail("TODO: C backend: implement 16-bit float lowering", .{}),
+                f32 => return writer.print("zig_bitcast_f32_u32(0x{x})", .{v}),
+                f64 => return writer.print("zig_bitcast_f64_u64(0x{x})", .{v}),
+                else => unreachable,
+            }
+        } else {
+            return writer.print("{x}", .{v});
+        }
+    }
+
+    fn renderFloat128(
+        writer: anytype,
+        val: f128,
+    ) error{ OutOfMemory, AnalysisFail }!void {
+        try writer.print("zig_bitcast_f128_u128(", .{});
+        try renderInt128(writer, @bitCast(u128, val));
+        try writer.print(")", .{});
+    }
+
     fn renderValue(
         dg: *DeclGen,
         writer: anytype,
@@ -605,19 +650,13 @@ pub const DeclGen = struct {
                 },
             },
             .Float => {
-                if (ty.floatBits(dg.module.getTarget()) <= 64) {
-                    if (std.math.isNan(val.toFloat(f64)) or std.math.isInf(val.toFloat(f64))) {
-                        // just generate a bit cast (exactly like we do in airBitcast)
-                        switch (ty.tag()) {
-                            .f32 => return writer.print("zig_bitcast_f32_u32(0x{x})", .{@bitCast(u32, val.toFloat(f32))}),
-                            .f64 => return writer.print("zig_bitcast_f64_u64(0x{x})", .{@bitCast(u64, val.toFloat(f64))}),
-                            else => return dg.fail("TODO float types > 64 bits are not support in renderValue() as of now", .{}),
-                        }
-                    } else {
-                        return writer.print("{x}", .{val.toFloat(f64)});
-                    }
+                switch (ty.tag()) {
+                    .f16 => return dg.renderSmallFloat(f16, writer, val),
+                    .f32 => return dg.renderSmallFloat(f32, writer, val),
+                    .f64 => return dg.renderSmallFloat(f64, writer, val),
+                    .f128 => return renderFloat128(writer, val.toFloat(f128)),
+                    else => unreachable,
                 }
-                return dg.fail("TODO: C backend: implement lowering large float values", .{});
             },
             .Pointer => switch (val.tag()) {
                 .null_value => try writer.writeAll("NULL"),
@@ -1295,11 +1334,11 @@ pub const DeclGen = struct {
             },
             .Float => {
                 switch (t.tag()) {
+                    .f16 => return dg.fail("TODO: C backend: implement float type f16", .{}),
                     .f32 => try w.writeAll("float"),
                     .f64 => try w.writeAll("double"),
+                    .f128 => try w.writeAll("float128_t"),
                     .c_longdouble => try w.writeAll("long double"),
-                    .f16 => return dg.fail("TODO: C backend: implement float type f16", .{}),
-                    .f128 => return dg.fail("TODO: C backend: implement float type f128", .{}),
                     else => unreachable,
                 }
             },

src/link/C/zig.h

@@ -165,6 +165,17 @@
 
 #define int128_t __int128
 #define uint128_t unsigned __int128
+
+#if defined(__aarch64__)
+#define ZIG_HAS_FLOAT128
+#define float128_t long double
+#elif defined(__FreeBSD__) || defined(__APPLE__)
+#define float128_t ZIG_UNSUPPORTED_SYMBOL_ON_TARGET_float128_t
+#else
+#define ZIG_HAS_FLOAT128
+#define float128_t __float128
+#endif
+
 ZIG_EXTERN_C void *memcpy (void *ZIG_RESTRICT, const void *ZIG_RESTRICT, size_t);
 ZIG_EXTERN_C void *memset (void *, int, size_t);
 
@@ -408,6 +419,14 @@ static inline double zig_bitcast_f64_u64(uint64_t arg) {
     return dest;
 }
 
+#if defined(ZIG_HAS_FLOAT128)
+static inline float128_t zig_bitcast_f128_u128(uint128_t arg) {
+    float128_t dest;
+    memcpy(&dest, &arg, sizeof dest);
+    return dest;
+}
+#endif
+
 #define zig_add_sat_u(ZT, T) static inline T zig_adds_##ZT(T x, T y, T max) { \
     return (x > max - y) ? max : x + y; \
 }

src/value.zig

@@ -2897,7 +2897,7 @@ pub const Value = extern union {
     pub fn floatToIntScalar(val: Value, arena: Allocator, int_ty: Type, target: Target) error{ FloatCannotFit, OutOfMemory }!Value {
         const Limb = std.math.big.Limb;
 
-        var value = val.toFloat(f64); // TODO: f128 ?
+        var value = val.toFloat(f128);
         if (std.math.isNan(value) or std.math.isInf(value)) {
             return error.FloatCannotFit;
         }
@@ -2909,7 +2909,7 @@ pub const Value = extern union {
 
         var rational = try std.math.big.Rational.init(arena);
         defer rational.deinit();
-        rational.setFloat(f64, floored) catch |err| switch (err) {
+        rational.setFloat(f128, floored) catch |err| switch (err) {
             error.NonFiniteFloat => unreachable,
             error.OutOfMemory => return error.OutOfMemory,
         };

test/behavior/floatop.zig

@@ -696,3 +696,53 @@ test "f128 at compile time is lossy" {
 
     try expect(@as(f128, 10384593717069655257060992658440192.0) + 1 == 10384593717069655257060992658440192.0);
 }
+
+test "f128 special values" {
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
+    if (builtin.cpu.arch == .i386) return error.SkipZigTest; // TODO
+
+    const f128_true_min = @bitCast(f128, @as(u128, 0x00000000000000000000000000000001));
+    const f128_min = @bitCast(f128, @as(u128, 0x00010000000000000000000000000000));
+    const f128_max = @bitCast(f128, @as(u128, 0x7ffeffffffffffffffffffffffffffff));
+    const f128_inf = @bitCast(f128, @as(u128, 0x7fff0000000000000000000000000000));
+    const f128_nan = @bitCast(f128, @as(u128, 0x7fff0000000000000000000000000001));
+
+    var buf = f128_true_min;
+    try expect(f128_true_min == buf);
+
+    buf = f128_min;
+    try expect(f128_min == buf);
+
+    buf = f128_max;
+    try expect(f128_max == buf);
+
+    buf = -f128_max;
+    try expect(-f128_max == buf);
+
+    buf = 0;
+    try expect(@as(f128, 0) == buf);
+
+    buf = -0;
+    try expect(@as(f128, -0) == buf);
+
+    buf = -1;
+    try expect(@as(f128, -1) == buf);
+
+    buf = @as(f128, math.f64_max) + 42.0;
+    try expect(@floatCast(f64, buf - 42.0) == math.f64_max);
+
+    buf = @as(f128, math.f64_min) - f128_min;
+    try expect(@floatCast(f64, buf + f128_min) == math.f64_min);
+
+    buf = f128_inf;
+    try expect(f128_inf == buf);
+
+    buf = -f128_inf;
+    try expect(-f128_inf == buf);
+
+    buf = f128_nan;
+    try expect(math.isNan(buf));
+}