0556a2ba53
Finishes cleanups that I started in other commits in this branch. * Use common.linkage for all exports instead of redoing the logic in each file. * Remove pointless `@setRuntimeSafety` calls. * Avoid redundantly exporting multiple versions of functions. For example, if PPC wants `ceilf128` then don't also export `ceilq`; similarly if ARM wants `__aeabi_ddiv` then don't also export `__divdf3`. * Use `inline` for helper functions instead of making inline calls at callsites.
48 lines
1.6 KiB
Zig
48 lines
1.6 KiB
Zig
//! 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 });
|
|
@export(__subodi4, .{ .name = "__subodi4", .linkage = common.linkage });
|
|
@export(__suboti4, .{ .name = "__suboti4", .linkage = common.linkage });
|
|
}
|
|
|
|
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;
|
|
var 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 occured, 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");
|
|
}
|