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
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
|
//
// The Zig compiler provides "builtin" functions. You've already
// gotten used to seeing an @import() at the top of every
// Ziglings exercise.
//
// We've also seen @intCast() in "016_for2.zig", "058_quiz7.zig";
// and @enumToInt() in "036_enums2.zig".
//
// Builtins are special because they are intrinsic to the Zig
// language itself (as opposed to being provided in the standard
// library). They are also special because they can provide
// functionality that is only possible with help from the
// compiler, such as type introspection (the ability to examine
// type properties from within a program).
//
// Zig currently contains 101 builtin functions. We're certainly
// not going to cover them all, but we can look at some
// interesting ones.
//
// Before we begin, know that many builtin functions have
// parameters marked as "comptime". It's probably fairly clear
// what we mean when we say that these parameters need to be
// "known at compile time." But rest assured we'll be doing the
// "comptime" subject real justice soon.
//
const print = @import("std").debug.print;
pub fn main() void {
// The first builtin, alphabetically, is:
//
// @addWithOverflow(comptime T: type, a: T, b: T, result: *T) bool
// * 'T' will be the type of the other parameters.
// * 'a' and 'b' are numbers of the type T.
// * 'result' is a pointer to space you're providing of type T.
// * The return value is true if the addition resulted in a
// value over or under the capacity of type T.
//
// Let's try it with a tiny 4-bit integer size to make it clear:
const a: u4 = 0b1101;
const b: u4 = 0b0101;
var my_result: u4 = undefined;
var overflowed: bool = undefined;
overflowed = @addWithOverflow(u4, a, b, &my_result);
//
// The print() below will produce: "1101 + 0101 = 0010 (true)".
// Let's make sense of this answer by counting up from 1101:
//
// Overflowed?
// 1101 + 1 = 1110 No.
// 1110 + 1 = 1111 No.
// 1111 + 1 = 0000 Yes! (Real answer is 10000)
// 0000 + 1 = 0001 Yes!
// 0001 + 1 = 0010 Yes!
//
// Also, check out our fancy formatting! b:0>4 means, "print
// as a binary number, zero-pad right-aligned four digits."
print("{b:0>4} + {b:0>4} = {b:0>4} ({})", .{ a, b, my_result, overflowed });
print(". Furthermore, ", .{});
// Here's a fun one:
//
// @bitReverse(comptime T: type, integer: T) T
// * 'T' will be the type of the input and output.
// * 'integer' is the value to reverse.
// * The return value will be the same type with the
// value's bits reversed!
//
// Now it's your turn. See if you can fix this attempt to use
// this builtin to reverse the bits of a u8 integer.
const input: u8 = 0b11110000;
const tupni: u8 = @bitReverse(input);
print("{b:0>8} backwards is {b:0>8}.\n", .{ input, tupni });
}
|
