compiler_rt: add __negvsi2, __negvdi2, __negvti2

- neg can only overflow, if a == MIN
- case `-0` is properly handled by hardware, so overflow check by comparing
  `a == MIN` is sufficient
- tests: MIN, MIN+1, MIN+4, -42, -7, -1, 0, 1, 7..

See #1290

CMakeLists.txt

@@ -500,6 +500,7 @@ set(ZIG_STAGE2_SOURCES
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/multi3.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/negXf2.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/negXi2.zig"
+    "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/negv.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/os_version_check.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/parity.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/popcount.zig"

lib/std/special/compiler_rt.zig

@@ -423,6 +423,12 @@ comptime {
         @export(__absvdi2, .{ .name = "__absvdi2", .linkage = linkage });
         const __absvti2 = @import("compiler_rt/absv.zig").__absvti2;
         @export(__absvti2, .{ .name = "__absvti2", .linkage = linkage });
+        const __negvsi2 = @import("compiler_rt/negv.zig").__negvsi2;
+        @export(__negvsi2, .{ .name = "__negvsi2", .linkage = linkage });
+        const __negvdi2 = @import("compiler_rt/negv.zig").__negvdi2;
+        @export(__negvdi2, .{ .name = "__negvdi2", .linkage = linkage });
+        const __negvti2 = @import("compiler_rt/negv.zig").__negvti2;
+        @export(__negvti2, .{ .name = "__negvti2", .linkage = linkage });
 
         // missing: Integral arithmetic which returns if overflow
 

lib/std/special/compiler_rt/negv.zig

@@ -0,0 +1,31 @@
+// negv - negate oVerflow
+// * @panic, if result can not be represented
+// - negvXi4_generic for unoptimized version
+
+// assume -0 == 0 is gracefully handled by the hardware
+fn negvXi_generic(comptime ST: type) fn (a: ST) callconv(.C) ST {
+    return struct {
+        fn f(a: ST) callconv(.C) ST {
+            const UT = switch (ST) {
+                i32 => u32,
+                i64 => u64,
+                i128 => u128,
+                else => unreachable,
+            };
+            const N: UT = @bitSizeOf(ST);
+            const min: ST = @bitCast(ST, (@as(UT, 1) << (N - 1)));
+            if (a == min)
+                @panic("compiler_rt negv: overflow");
+            return -a;
+        }
+    }.f;
+}
+pub const __negvsi2 = negvXi_generic(i32);
+pub const __negvdi2 = negvXi_generic(i64);
+pub const __negvti2 = negvXi_generic(i128);
+
+test {
+    _ = @import("negvsi2_test.zig");
+    _ = @import("negvdi2_test.zig");
+    _ = @import("negvti2_test.zig");
+}

lib/std/special/compiler_rt/negvdi2_test.zig

@@ -0,0 +1,30 @@
+const negv = @import("negv.zig");
+const testing = @import("std").testing;
+
+fn test__negvdi2(a: i64, expected: i64) !void {
+    var result = negv.__negvdi2(a);
+    try testing.expectEqual(expected, result);
+}
+
+test "negvdi2" {
+    // -2^63 <= i64 <= 2^63-1
+    // 2^63 = 9223372036854775808
+    // 2^63-1 = 9223372036854775807
+    // TODO write panic handler for testing panics
+    //try test__negvdi2(-9223372036854775808, -5); // tested with return -5; and panic
+    try test__negvdi2(-9223372036854775807, 9223372036854775807);
+    try test__negvdi2(-9223372036854775806, 9223372036854775806);
+    try test__negvdi2(-9223372036854775805, 9223372036854775805);
+    try test__negvdi2(-9223372036854775804, 9223372036854775804);
+    try test__negvdi2(-42, 42);
+    try test__negvdi2(-7, 7);
+    try test__negvdi2(-1, 1);
+    try test__negvdi2(0, 0);
+    try test__negvdi2(1, -1);
+    try test__negvdi2(7, -7);
+    try test__negvdi2(42, -42);
+    try test__negvdi2(9223372036854775804, -9223372036854775804);
+    try test__negvdi2(9223372036854775805, -9223372036854775805);
+    try test__negvdi2(9223372036854775806, -9223372036854775806);
+    try test__negvdi2(9223372036854775807, -9223372036854775807);
+}

lib/std/special/compiler_rt/negvsi2_test.zig

@@ -0,0 +1,30 @@
+const negv = @import("negv.zig");
+const testing = @import("std").testing;
+
+fn test__negvsi2(a: i32, expected: i32) !void {
+    var result = negv.__negvsi2(a);
+    try testing.expectEqual(expected, result);
+}
+
+test "negvsi2" {
+    // -2^31 <= i32 <= 2^31-1
+    // 2^31 = 2147483648
+    // 2^31-1 = 2147483647
+    // TODO write panic handler for testing panics
+    //try test__negvsi2(-2147483648, -5); // tested with return -5; and panic
+    try test__negvsi2(-2147483647, 2147483647);
+    try test__negvsi2(-2147483646, 2147483646);
+    try test__negvsi2(-2147483645, 2147483645);
+    try test__negvsi2(-2147483644, 2147483644);
+    try test__negvsi2(-42, 42);
+    try test__negvsi2(-7, 7);
+    try test__negvsi2(-1, 1);
+    try test__negvsi2(0, 0);
+    try test__negvsi2(1, -1);
+    try test__negvsi2(7, -7);
+    try test__negvsi2(42, -42);
+    try test__negvsi2(2147483644, -2147483644);
+    try test__negvsi2(2147483645, -2147483645);
+    try test__negvsi2(2147483646, -2147483646);
+    try test__negvsi2(2147483647, -2147483647);
+}

lib/std/special/compiler_rt/negvti2_test.zig

@@ -0,0 +1,30 @@
+const negv = @import("negv.zig");
+const testing = @import("std").testing;
+
+fn test__negvti2(a: i128, expected: i128) !void {
+    var result = negv.__negvti2(a);
+    try testing.expectEqual(expected, result);
+}
+
+test "negvti2" {
+    // -2^127 <= i128 <= 2^127-1
+    // 2^127 = 170141183460469231731687303715884105728
+    // 2^127+1 = 170141183460469231731687303715884105727
+    // TODO write panic handler for testing panics
+    //try test__negvti2(-170141183460469231731687303715884105728, -5); // tested with return -5; and panic
+    try test__negvti2(-170141183460469231731687303715884105727, 170141183460469231731687303715884105727);
+    try test__negvti2(-170141183460469231731687303715884105726, 170141183460469231731687303715884105726);
+    try test__negvti2(-170141183460469231731687303715884105725, 170141183460469231731687303715884105725);
+    try test__negvti2(-170141183460469231731687303715884105724, 170141183460469231731687303715884105724);
+    try test__negvti2(-42, 42);
+    try test__negvti2(-7, 7);
+    try test__negvti2(-1, 1);
+    try test__negvti2(0, 0);
+    try test__negvti2(1, -1);
+    try test__negvti2(7, -7);
+    try test__negvti2(42, -42);
+    try test__negvti2(170141183460469231731687303715884105724, -170141183460469231731687303715884105724);
+    try test__negvti2(170141183460469231731687303715884105725, -170141183460469231731687303715884105725);
+    try test__negvti2(170141183460469231731687303715884105726, -170141183460469231731687303715884105726);
+    try test__negvti2(170141183460469231731687303715884105727, -170141183460469231731687303715884105727);
+}