79 lines
2.4 KiB
Zig
79 lines
2.4 KiB
Zig
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const std = @import("std");
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const testing = std.testing;
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const GraphemeCache = @This();
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/// the underlying storage for graphemes
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buf: [1024 * 4]u8 = undefined,
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// the start index of the next grapheme
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idx: usize = 0,
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/// the cache of graphemes. This allows up to 1024 graphemes with 4 codepoints
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/// each
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grapheme_buf: [1024]Grapheme = undefined,
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// index of our next grapheme
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g_idx: u21 = 0,
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pub const UNICODE_MAX = 1_114_112;
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const Grapheme = struct {
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// codepoint is an index into the internal storage
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codepoint: u21,
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start: usize,
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end: usize,
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};
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/// put a slice of bytes in the cache as a grapheme
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pub fn put(self: *GraphemeCache, bytes: []const u8) !u21 {
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// See if we already have these bytes. It's a likely case that if we get one
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// grapheme, we'll get it again. So this will save a lot of storage and is
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// most likely worth the cost as it's pretty rare
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for (self.grapheme_buf) |grapheme| {
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const g_bytes = self.buf[grapheme.start..grapheme.end];
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if (std.mem.eql(u8, g_bytes, bytes)) {
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return grapheme.codepoint;
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}
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}
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if (self.idx + bytes.len > self.buf.len) return error.OutOfGraphemeBufferMemory;
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if (self.g_idx + 1 > self.grapheme_buf.len) return error.OutOfGraphemeMemory;
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// copy the grapheme to our storage
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@memcpy(self.buf[self.idx .. self.idx + bytes.len], bytes);
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const g = Grapheme{
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// assign a codepoint that is always outside of valid unicode
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.codepoint = self.g_idx + UNICODE_MAX + 1,
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.start = self.idx,
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.end = self.idx + bytes.len,
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};
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self.grapheme_buf[self.g_idx] = g;
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self.g_idx += 1;
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self.idx += bytes.len;
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return g.codepoint;
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}
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/// get the slice of bytes for a given grapheme
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pub fn get(self: *GraphemeCache, cp: u21) ![]const u8 {
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if (cp < (UNICODE_MAX + 1)) return error.InvalidGraphemeIndex;
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const idx: usize = cp - UNICODE_MAX - 1;
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if (idx > self.g_idx) return error.InvalidGraphemeIndex;
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const g = self.grapheme_buf[idx];
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return self.buf[g.start..g.end];
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}
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test "GraphemeCache: roundtrip" {
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var cache: GraphemeCache = .{};
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const cp = try cache.put("abc");
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const bytes = try cache.get(cp);
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try testing.expectEqualStrings("abc", bytes);
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const cp_2 = try cache.put("abc");
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try testing.expectEqual(cp, cp_2);
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const cp_3 = try cache.put("def");
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try testing.expectEqual(cp + 1, cp_3);
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}
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