54 lines
1.8 KiB
Zig
54 lines
1.8 KiB
Zig
const std = @import("std");
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const assert = std.debug.assert;
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const Allocator = std.mem.Allocator;
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const ArrayList = std.ArrayList;
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// rounds up an int to the nearest factor of nbits.
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pub fn roundUp(comptime T: type, comptime nbits: u8, n: T) T {
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comptime assert(nbits < @bitSizeOf(T));
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const factor = comptime (1 << nbits) - 1;
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return ((n + factor) & ~@as(T, factor));
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}
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// rounds up an integer to the nearest factor of nbits and returns the
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// difference (padding)
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pub fn until(comptime T: type, comptime nbits: u8, n: T) T {
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return roundUp(T, nbits, n) - n;
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}
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// arrayList adds padding to an ArrayList(u8) for a given number of nbits
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pub fn arrayList(arr: *ArrayList(u8), comptime nbits: u8) Allocator.Error!void {
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const padding = until(u64, nbits, arr.items.len);
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try arr.*.appendNTimes(0, padding);
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}
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const testing = std.testing;
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test "padding" {
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try testing.expectEqual(until(u12, 2, 0), 0);
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try testing.expectEqual(until(u12, 2, 1), 3);
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try testing.expectEqual(until(u12, 2, 2), 2);
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try testing.expectEqual(until(u12, 2, 3), 1);
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try testing.expectEqual(until(u12, 2, 4), 0);
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try testing.expectEqual(until(u12, 2, 40), 0);
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try testing.expectEqual(until(u12, 2, 41), 3);
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try testing.expectEqual(until(u12, 2, 42), 2);
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try testing.expectEqual(until(u12, 2, 43), 1);
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try testing.expectEqual(until(u12, 2, 44), 0);
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try testing.expectEqual(until(u12, 2, 4091), 1);
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try testing.expectEqual(until(u12, 2, 4092), 0);
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}
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test "arrayList" {
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var buf = try ArrayList(u8).initCapacity(testing.allocator, 16);
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defer buf.deinit();
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buf.appendAssumeCapacity(1);
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try arrayList(&buf, 3);
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try testing.expectEqual(buf.items.len, 8);
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buf.appendAssumeCapacity(2);
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try arrayList(&buf, 10);
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try testing.expectEqual(buf.items.len, 1024);
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}
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