addvsi3.zig

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Code

const compiler_rt = @import("../compiler_rt.zig");
const symbol = compiler_rt.symbol;
const testing = @import("std").testing;

comptime {
    symbol(&__addvsi3, "__addvsi3");
}

pub fn __addvsi3(a: i32, b: i32) callconv(.c) i32 {
    const sum = a +% b;
    // Overflow occurred iff both operands have the same sign, and the sign of the sum does
    // not match it. In other words, iff the sum sign is not the sign of either operand.
    if (((sum ^ a) & (sum ^ b)) < 0) @panic("compiler-rt: integer overflow");
    return sum;
}

test "addvsi3" {
    // const min: i32 = -2147483648
    // const max: i32 = 2147483647
    // TODO write panic handler for testing panics
    // try test__addvsi3(-2147483648, -1, -1); // panic
    // try test__addvsi3(2147483647, 1, 1);  // panic
    try testing.expectEqual(-2147483648, __addvsi3(-2147483647, -1));
    try testing.expectEqual(2147483647, __addvsi3(2147483646, 1));
}