1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
|
//! subo - subtract overflow
//! * return a-%b.
//! * return if a-b overflows => 1 else => 0
//! - suboXi4_generic as default
const std = @import("std");
const builtin = @import("builtin");
const common = @import("common.zig");
pub const panic = common.panic;
comptime {
@export(&__subosi4, .{ .name = "__subosi4", .linkage = common.linkage, .visibility = common.visibility });
@export(&__subodi4, .{ .name = "__subodi4", .linkage = common.linkage, .visibility = common.visibility });
@export(&__suboti4, .{ .name = "__suboti4", .linkage = common.linkage, .visibility = common.visibility });
}
pub fn __subosi4(a: i32, b: i32, overflow: *c_int) callconv(.c) i32 {
return suboXi4_generic(i32, a, b, overflow);
}
pub fn __subodi4(a: i64, b: i64, overflow: *c_int) callconv(.c) i64 {
return suboXi4_generic(i64, a, b, overflow);
}
pub fn __suboti4(a: i128, b: i128, overflow: *c_int) callconv(.c) i128 {
return suboXi4_generic(i128, a, b, overflow);
}
inline fn suboXi4_generic(comptime ST: type, a: ST, b: ST, overflow: *c_int) ST {
overflow.* = 0;
const sum: ST = a -% b;
// Hackers Delight: section Overflow Detection, subsection Signed Add/Subtract
// Let sum = a -% b == a - b - carry == wraparound subtraction.
// Overflow in a-b-carry occurs, iff a and b have opposite signs
// and the sign of a-b-carry is opposite of a (or equivalently same as b).
// Faster routine: res = (a ^ b) & (sum ^ a)
// Slower routine: res = (sum^a) & ~(sum^b)
// Overflow occurred, iff (res < 0)
if (((a ^ b) & (sum ^ a)) < 0)
overflow.* = 1;
return sum;
}
test {
_ = @import("subosi4_test.zig");
_ = @import("subodi4_test.zig");
_ = @import("suboti4_test.zig");
}
|
