tiny.filigree.layout.class

1const std = @import("std");23const binary = @import("binary.zig");4const LayoutError = binary.LayoutError;5const hasBytes = binary.hasBytes;6const readU16 = binary.readU16;78pub const ClassDef = union(enum) {9    format_1: ClassDefFormat1,10    format_2: ClassDefFormat2,1112    pub fn init(data: []const u8, offset: usize) LayoutError!ClassDef {13        if (!hasBytes(data, offset, 2)) return error.InvalidLayout;14        return switch (try readU16(data, offset)) {15            1 => .{ .format_1 = try ClassDefFormat1.init(data, offset) },16            2 => .{ .format_2 = try ClassDefFormat2.init(data, offset) },17            else => error.UnsupportedClassDef,18        };19    }2021    pub fn class(self: ClassDef, data: []const u8, glyph_id: u32) LayoutError!u16 {22        return switch (self) {23            .format_1 => |format| format.class(data, glyph_id),24            .format_2 => |format| format.class(data, glyph_id),25        };26    }27};2829pub const ClassDefFormat1 = struct {30    start_glyph_id: u16,31    class_value_offset: usize,32    glyph_count: u16,3334    fn init(data: []const u8, offset: usize) LayoutError!ClassDefFormat1 {35        if (!hasBytes(data, offset, 6)) return error.InvalidLayout;36        const glyph_count = try readU16(data, offset + 4);37        const array_offset = offset + 6;38        const array_len = @as(usize, glyph_count) * 2;39        if (!hasBytes(data, array_offset, array_len)) return error.InvalidLayout;40        return .{41            .start_glyph_id = try readU16(data, offset + 2),42            .class_value_offset = array_offset,43            .glyph_count = glyph_count,44        };45    }4647    fn class(self: ClassDefFormat1, data: []const u8, glyph_id: u32) LayoutError!u16 {48        if (glyph_id > std.math.maxInt(u16)) return 0;49        const glyph: u16 = @intCast(glyph_id);50        if (glyph < self.start_glyph_id) return 0;51        const index = @as(usize, glyph - self.start_glyph_id);52        if (index >= self.glyph_count) return 0;53        return try readU16(data, self.class_value_offset + index * 2);54    }55};5657pub const ClassDefFormat2 = struct {58    class_range_array_offset: usize,59    class_range_count: u16,6061    fn init(data: []const u8, offset: usize) LayoutError!ClassDefFormat2 {62        if (!hasBytes(data, offset, 4)) return error.InvalidLayout;63        const range_count = try readU16(data, offset + 2);64        const array_offset = offset + 4;65        const array_len = @as(usize, range_count) * 6;66        if (!hasBytes(data, array_offset, array_len)) return error.InvalidLayout;67        var previous_end: ?u16 = null;68        for (0..range_count) |i| {69            const record = array_offset + i * 6;70            const start = try readU16(data, record);71            const end = try readU16(data, record + 2);72            if (start > end) return error.InvalidLayout;73            if (previous_end) |seen| {74                if (start <= seen) return error.InvalidLayout;75            }76            previous_end = end;77        }78        return .{79            .class_range_array_offset = array_offset,80            .class_range_count = range_count,81        };82    }8384    fn class(self: ClassDefFormat2, data: []const u8, glyph_id: u32) LayoutError!u16 {85        if (glyph_id > std.math.maxInt(u16)) return 0;86        const glyph: u16 = @intCast(glyph_id);87        var left: usize = 0;88        var right: usize = self.class_range_count;89        while (left < right) {90            const mid = left + (right - left) / 2;91            const record = self.class_range_array_offset + mid * 6;92            const start = try readU16(data, record);93            const end = try readU16(data, record + 2);94            if (glyph < start) {95                right = mid;96            } else if (glyph > end) {97                left = mid + 1;98            } else {99                return try readU16(data, record + 4);100            }101        }102        return 0;103    }104};105106test "ClassDef format 1 maps consecutive glyph classes" {107    const data = [_]u8{108        0, 1,109        0, 5,110        0, 3,111        0, 1,112        0, 7,113        0, 2,114    };115    const class_def = try ClassDef.init(&data, 0);116    try std.testing.expectEqual(@as(u16, 0), try class_def.class(&data, 4));117    try std.testing.expectEqual(@as(u16, 1), try class_def.class(&data, 5));118    try std.testing.expectEqual(@as(u16, 7), try class_def.class(&data, 6));119    try std.testing.expectEqual(@as(u16, 2), try class_def.class(&data, 7));120    try std.testing.expectEqual(@as(u16, 0), try class_def.class(&data, 8));121}122123test "ClassDef format 2 maps class ranges" {124    const data = [_]u8{125        0, 2,126        0, 2,127        0, 10,128        0, 12,129        0, 4,130        0, 30,131        0, 31,132        0, 8,133    };134    const class_def = try ClassDef.init(&data, 0);135    try std.testing.expectEqual(@as(u16, 4), try class_def.class(&data, 10));136    try std.testing.expectEqual(@as(u16, 4), try class_def.class(&data, 12));137    try std.testing.expectEqual(@as(u16, 8), try class_def.class(&data, 31));138    try std.testing.expectEqual(@as(u16, 0), try class_def.class(&data, 13));139    try std.testing.expectEqual(@as(u16, 0), try class_def.class(&data, 0x1_0000));140}141142test "ClassDef honors nonzero table offsets" {143    const data = [_]u8{144        0xaa, 0xbb,145        0,    1,146        0,    7,147        0,    1,148        0,    5,149    };150    const class_def = try ClassDef.init(&data, 2);151    try std.testing.expectEqual(@as(u16, 5), try class_def.class(&data, 7));152}153154test "ClassDef rejects unsupported format" {155    const data = [_]u8{ 0, 3 };156    try std.testing.expectError(error.UnsupportedClassDef, ClassDef.init(&data, 0));157}

1pub const class = @import("class.zig");