Zig 0.17.0-dev (Split by item)

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storeBits

Store bits using native endianness when value spans multiple bytes. On big endian architectures:

For a given value, the bits of an earlier byte are more significant than the bits of subsequent bytes.
bit_offset uses MSb 0 bit numbering. On little endian architectures:
For a given value, the bits of an earlier byte are less significant than the bits of subsequent bytes.
bit_offset uses LSb 0 bit numbering.

Configuration.storeBits

pub fn storeBits(comptime Int: type, buffer: []Int, bit_offset: usize, value: anytype) void

File

lib/std/Build/Configuration.zig:3524

Code

pub fn storeBits(comptime Int: type, buffer: []Int, bit_offset: usize, value: anytype) void {
    const Value = @TypeOf(value);
    const ValueInt = @Int(.unsigned, @bitSizeOf(Value));
    const value_int: ValueInt = @bitCast(value);
    const index = bit_offset / @bitSizeOf(Int);
    const small_bit_offset = bit_offset % @bitSizeOf(Int);
    const available_bits = @bitSizeOf(Int) - small_bit_offset;
    if (available_bits >= @bitSizeOf(ValueInt)) {
        const shift = switch (native_endian) {
            .little => small_bit_offset,
            .big => available_bits - @bitSizeOf(ValueInt),
        };
        buffer[index] &= ~(((@as(Int, 1) << @intCast(@bitSizeOf(Value))) - 1) << @intCast(shift));
        buffer[index] |= @as(Int, value_int) << @intCast(shift);
    } else {
        const DoubleInt = @Int(.unsigned, @bitSizeOf(Int) * 2);
        const shift = switch (native_endian) {
            .little => small_bit_offset,
            .big => @bitSizeOf(DoubleInt) - small_bit_offset - @bitSizeOf(ValueInt),
        };
        const ptr: *align(@alignOf(Int)) DoubleInt = @ptrCast(buffer[index..][0..2]);
        ptr.* &= ~(((@as(DoubleInt, 1) << @intCast(@bitSizeOf(Value))) - 1) << @intCast(shift));
        ptr.* |= @as(DoubleInt, value_int) << @intCast(shift);
    }
}