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const subo = @import("subo.zig");
const std = @import("std");
const testing = std.testing;
const math = std.math;
fn test__subodi4(a: i64, b: i64) !void {
var result_ov: c_int = undefined;
var expected_ov: c_int = undefined;
const result = subo.__subodi4(a, b, &result_ov);
const expected: i64 = simple_subodi4(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_subodi4(a: i64, b: i64, overflow: *c_int) i64 {
overflow.* = 0;
const min: i64 = math.minInt(i64);
const max: i64 = math.maxInt(i64);
if (((b > 0) and (a < min + b)) or
((b < 0) and (a > max + b)))
overflow.* = 1;
return a -% b;
}
test "subodi3" {
const min: i64 = math.minInt(i64);
const max: i64 = math.maxInt(i64);
var i: i64 = 1;
while (i < max) : (i *|= 2) {
try test__subodi4(i, i);
try test__subodi4(-i, -i);
try test__subodi4(i, -i);
try test__subodi4(-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__subodi4(0, 0);
try test__subodi4(min, min);
try test__subodi4(max, max);
try test__subodi4(0, min);
try test__subodi4(0, max);
try test__subodi4(min, 0);
try test__subodi4(max, 0);
try test__subodi4(min, max);
try test__subodi4(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__subodi4(min + 1, min);
try test__subodi4(max - 1, max);
try test__subodi4(1, min);
try test__subodi4(-1, min);
try test__subodi4(-1, max);
try test__subodi4(1, max);
try test__subodi4(min, 1);
try test__subodi4(min, -1);
try test__subodi4(max, -1);
try test__subodi4(max, 1);
}
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