mirror of
https://github.com/ziglang/zig.git
synced 2024-11-27 07:32:44 +00:00
82 lines
2.4 KiB
Zig
82 lines
2.4 KiB
Zig
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const subo = @import("subo.zig");
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const std = @import("std");
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const testing = std.testing;
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const math = std.math;
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fn test__suboti4(a: i128, b: i128) !void {
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var result_ov: c_int = undefined;
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var expected_ov: c_int = undefined;
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var result = subo.__suboti4(a, b, &result_ov);
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var expected: i128 = simple_suboti4(a, b, &expected_ov);
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try testing.expectEqual(expected, result);
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try testing.expectEqual(expected_ov, result_ov);
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}
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// 2 cases on evaluating `a-b`:
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// 1. `a-b` may underflow, iff b>0 && a<0 and a-b < min <=> a<min+b
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// 2. `a-b` may overflow, iff b<0 && a>0 and a-b > max <=> a>max+b
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// `-b` evaluation may overflow, iff b==min, but this is handled by the hardware
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pub fn simple_suboti4(a: i128, b: i128, overflow: *c_int) i128 {
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overflow.* = 0;
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const min: i128 = math.minInt(i128);
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const max: i128 = math.maxInt(i128);
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if (((b > 0) and (a < min + b)) or
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((b < 0) and (a > max + b)))
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overflow.* = 1;
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return a -% b;
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}
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test "suboti3" {
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const min: i128 = math.minInt(i128);
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const max: i128 = math.maxInt(i128);
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var i: i128 = 1;
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while (i < max) : (i *|= 2) {
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try test__suboti4(i, i);
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try test__suboti4(-i, -i);
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try test__suboti4(i, -i);
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try test__suboti4(-i, i);
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}
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// edge cases
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// 0 - 0 = 0
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// MIN - MIN = 0
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// MAX - MAX = 0
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// 0 - MIN overflow
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// 0 - MAX = MIN+1
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// MIN - 0 = MIN
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// MAX - 0 = MAX
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// MIN - MAX overflow
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// MAX - MIN overflow
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try test__suboti4(0, 0);
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try test__suboti4(min, min);
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try test__suboti4(max, max);
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try test__suboti4(0, min);
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try test__suboti4(0, max);
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try test__suboti4(min, 0);
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try test__suboti4(max, 0);
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try test__suboti4(min, max);
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try test__suboti4(max, min);
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// derived edge cases
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// MIN+1 - MIN = 1
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// MAX-1 - MAX = -1
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// 1 - MIN overflow
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// -1 - MIN = MAX
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// -1 - MAX = MIN
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// +1 - MAX = MIN+2
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// MIN - 1 overflow
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// MIN - -1 = MIN+1
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// MAX - 1 = MAX-1
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// MAX - -1 overflow
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try test__suboti4(min + 1, min);
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try test__suboti4(max - 1, max);
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try test__suboti4(1, min);
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try test__suboti4(-1, min);
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try test__suboti4(-1, max);
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try test__suboti4(1, max);
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try test__suboti4(min, 1);
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try test__suboti4(min, -1);
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try test__suboti4(max, -1);
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try test__suboti4(max, 1);
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}
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