Function generate [src]

Update this Huffman Code object to be the minimum code for the specified frequency count. freq An array of frequencies, in which frequency[i] gives the frequency of literal i. max_bits The maximum number of bits to use for any literal.

Prototype

pub fn generate(self: *HuffmanEncoder, freq: []u16, max_bits: u32) void

Parameters

self: *HuffmanEncoderfreq: []u16max_bits: u32

Source

  pub fn generate(self: *HuffmanEncoder, freq: []u16, max_bits: u32) void {
    var list = self.freq_cache[0 .. freq.len + 1];
    // Number of non-zero literals
    var count: u32 = 0;
    // Set list to be the set of all non-zero literals and their frequencies
    for (freq, 0..) |f, i| {
        if (f != 0) {
            list[count] = LiteralNode{ .literal = @as(u16, @intCast(i)), .freq = f };
            count += 1;
        } else {
            list[count] = LiteralNode{ .literal = 0x00, .freq = 0 };
            self.codes[i].len = 0;
        }
    }
    list[freq.len] = LiteralNode{ .literal = 0x00, .freq = 0 };

    list = list[0..count];
    if (count <= 2) {
        // Handle the small cases here, because they are awkward for the general case code. With
        // two or fewer literals, everything has bit length 1.
        for (list, 0..) |node, i| {
            // "list" is in order of increasing literal value.
            self.codes[node.literal] = .{
                .code = @intCast(i),
                .len = 1,
            };
        }
        return;
    }
    self.lfs = list;
    std.mem.sort(LiteralNode, self.lfs, {}, byFreq);

    // Get the number of literals for each bit count
    const bit_count = self.bitCounts(list, max_bits);
    // And do the assignment
    self.assignEncodingAndSize(bit_count, list);
}  