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const subo = @import("subo.zig");
const testing = @import("std").testing;
fn test__subosi4(a: i32, b: i32) !void {
var result_ov: c_int = undefined;
var expected_ov: c_int = undefined;
const result = subo.__subosi4(a, b, &result_ov);
const expected: i32 = simple_subosi4(a, b, &expected_ov);
try testing.expectEqual(expected, result);
try testing.expectEqual(expected_ov, result_ov);
}
// 2 cases on evaluating `a-b`:
// 1. `a-b` may underflow, iff b>0 && a<0 and a-b < min <=> a<min+b
// 2. `a-b` may overflow, iff b<0 && a>0 and a-b > max <=> a>max+b
// `-b` evaluation may overflow, iff b==min, but this is handled by the hardware
pub fn simple_subosi4(a: i32, b: i32, overflow: *c_int) i32 {
overflow.* = 0;
const min: i32 = -2147483648;
const max: i32 = 2147483647;
if (((b > 0) and (a < min + b)) or
((b < 0) and (a > max + b)))
overflow.* = 1;
return a -% b;
}
test "subosi3" {
// -2^31 <= i32 <= 2^31-1
// 2^31 = 2147483648
// 2^31-1 = 2147483647
const min: i32 = -2147483648;
const max: i32 = 2147483647;
var i: i32 = 1;
while (i < max) : (i *|= 2) {
try test__subosi4(i, i);
try test__subosi4(-i, -i);
try test__subosi4(i, -i);
try test__subosi4(-i, i);
}
// edge cases
// 0 - 0 = 0
// MIN - MIN = 0
// MAX - MAX = 0
// 0 - MIN overflow
// 0 - MAX = MIN+1
// MIN - 0 = MIN
// MAX - 0 = MAX
// MIN - MAX overflow
// MAX - MIN overflow
try test__subosi4(0, 0);
try test__subosi4(min, min);
try test__subosi4(max, max);
try test__subosi4(0, min);
try test__subosi4(0, max);
try test__subosi4(min, 0);
try test__subosi4(max, 0);
try test__subosi4(min, max);
try test__subosi4(max, min);
// derived edge cases
// MIN+1 - MIN = 1
// MAX-1 - MAX = -1
// 1 - MIN overflow
// -1 - MIN = MAX
// -1 - MAX = MIN
// +1 - MAX = MIN+2
// MIN - 1 overflow
// MIN - -1 = MIN+1
// MAX - 1 = MAX-1
// MAX - -1 overflow
try test__subosi4(min + 1, min);
try test__subosi4(max - 1, max);
try test__subosi4(1, min);
try test__subosi4(-1, min);
try test__subosi4(-1, max);
try test__subosi4(1, max);
try test__subosi4(min, 1);
try test__subosi4(min, -1);
try test__subosi4(max, -1);
try test__subosi4(max, 1);
}
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