33 lines
1.2 KiB
Zig
33 lines
1.2 KiB
Zig
const std = @import("std");
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const assert = std.debug.assert;
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// rounds up a u12 to the nearest factor of 4 and returns the difference
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// (padding)
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pub fn roundUpPadding(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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// rounds up a u12 to the nearest factor of 4.
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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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const testing = std.testing;
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test "padding" {
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try testing.expectEqual(roundUpPadding(u12, 2, 0), 0);
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try testing.expectEqual(roundUpPadding(u12, 2, 1), 3);
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try testing.expectEqual(roundUpPadding(u12, 2, 2), 2);
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try testing.expectEqual(roundUpPadding(u12, 2, 3), 1);
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try testing.expectEqual(roundUpPadding(u12, 2, 4), 0);
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try testing.expectEqual(roundUpPadding(u12, 2, 40), 0);
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try testing.expectEqual(roundUpPadding(u12, 2, 41), 3);
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try testing.expectEqual(roundUpPadding(u12, 2, 42), 2);
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try testing.expectEqual(roundUpPadding(u12, 2, 43), 1);
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try testing.expectEqual(roundUpPadding(u12, 2, 44), 0);
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try testing.expectEqual(roundUpPadding(u12, 2, 4091), 1);
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try testing.expectEqual(roundUpPadding(u12, 2, 4092), 0);
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}
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