Zig 0.17.0-dev (Split by item)

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loadBits

Loads bits using native endianness when value spans multiple bytes. On big endian architectures, bit_offset uses MSb 0 bit numbering. On little endian architectures, bit_offset uses LSb 0 bit numbering. See storeBits.

Configuration.loadBits

pub fn loadBits(comptime Int: type, buffer: []const Int, bit_offset: usize, comptime Result: type) Result

File

lib/std/Build/Configuration.zig:3488

Code

pub fn loadBits(comptime Int: type, buffer: []const Int, bit_offset: usize, comptime Result: type) Result {
    const index = bit_offset / @bitSizeOf(Int);
    const small_bit_offset = bit_offset % @bitSizeOf(Int);
    const ResultInt = @Int(.unsigned, @bitSizeOf(Result));
    switch (native_endian) {
        .little => {
            const result: ResultInt = @truncate(buffer[index] >> @intCast(small_bit_offset));
            const available_bits = @bitSizeOf(Int) - small_bit_offset;
            if (available_bits >= @bitSizeOf(ResultInt)) return @bitCast(result);
            const missing_bits = @bitSizeOf(ResultInt) - available_bits;
            const upper: ResultInt = @truncate(buffer[index + 1] & ((@as(usize, 1) << @intCast(missing_bits)) - 1));
            return @bitCast(result | (upper << @intCast(available_bits)));
        },
        .big => {
            const available_bits = @bitSizeOf(Int) - small_bit_offset;
            if (available_bits >= @bitSizeOf(ResultInt)) {
                const shift = available_bits - @bitSizeOf(ResultInt);
                const result: ResultInt = @truncate(buffer[index] >> @intCast(shift));
                return @bitCast(result);
            }
            const mask = (@as(Int, 1) << @intCast(available_bits)) - 1;
            const result: ResultInt = @intCast(buffer[index] & mask);
            const missing_bits = @bitSizeOf(ResultInt) - available_bits;
            const lower: ResultInt = @truncate(buffer[index + 1] >> @intCast(@bitSizeOf(Int) - missing_bits));
            return @bitCast((result << @intCast(missing_bits)) | lower);
        },
    }
}