subo.zig (1742B) - Raw
1 //! subo - subtract overflow 2 //! * return a-%b. 3 //! * return if a-b overflows => 1 else => 0 4 //! - suboXi4_generic as default 5 6 const std = @import("std"); 7 const builtin = @import("builtin"); 8 const common = @import("common.zig"); 9 10 pub const panic = common.panic; 11 12 comptime { 13 @export(&__subosi4, .{ .name = "__subosi4", .linkage = common.linkage, .visibility = common.visibility }); 14 @export(&__subodi4, .{ .name = "__subodi4", .linkage = common.linkage, .visibility = common.visibility }); 15 @export(&__suboti4, .{ .name = "__suboti4", .linkage = common.linkage, .visibility = common.visibility }); 16 } 17 18 pub fn __subosi4(a: i32, b: i32, overflow: *c_int) callconv(.c) i32 { 19 return suboXi4_generic(i32, a, b, overflow); 20 } 21 pub fn __subodi4(a: i64, b: i64, overflow: *c_int) callconv(.c) i64 { 22 return suboXi4_generic(i64, a, b, overflow); 23 } 24 pub fn __suboti4(a: i128, b: i128, overflow: *c_int) callconv(.c) i128 { 25 return suboXi4_generic(i128, a, b, overflow); 26 } 27 28 inline fn suboXi4_generic(comptime ST: type, a: ST, b: ST, overflow: *c_int) ST { 29 overflow.* = 0; 30 const sum: ST = a -% b; 31 // Hackers Delight: section Overflow Detection, subsection Signed Add/Subtract 32 // Let sum = a -% b == a - b - carry == wraparound subtraction. 33 // Overflow in a-b-carry occurs, iff a and b have opposite signs 34 // and the sign of a-b-carry is opposite of a (or equivalently same as b). 35 // Faster routine: res = (a ^ b) & (sum ^ a) 36 // Slower routine: res = (sum^a) & ~(sum^b) 37 // Overflow occurred, iff (res < 0) 38 if (((a ^ b) & (sum ^ a)) < 0) 39 overflow.* = 1; 40 return sum; 41 } 42 43 test { 44 _ = @import("subosi4_test.zig"); 45 _ = @import("subodi4_test.zig"); 46 _ = @import("suboti4_test.zig"); 47 }