Function base64::engine::general_purpose::decode::decode_helper

pub(crate) fn decode_helper(
    input: &[u8],
    estimate: GeneralPurposeEstimate,
    output: &mut [u8],
    decode_table: &[u8; 256],
    decode_allow_trailing_bits: bool,
    padding_mode: DecodePaddingMode,
) -> Result<DecodeMetadata, DecodeSliceError>

Helper to avoid duplicating num_chunks calculation, which is costly on short inputs. Returns the decode metadata, or an error.