Function ExpandArray

src/crypto/equihash.cpp:77–118

}

void ExpandArray(const unsigned char* in, size_t in_len,
                 unsigned char* out, size_t out_len,
                 size_t bit_len, size_t byte_pad)
{
    assert(bit_len >= 8);
    assert(8*sizeof(uint32_t) >= 7+bit_len);

    size_t out_width { (bit_len+7)/8 + byte_pad };
    assert(out_len == 8*out_width*in_len/bit_len);

    uint32_t bit_len_mask { ((uint32_t)1 << bit_len) - 1 };

    // The acc_bits least-significant bits of acc_value represent a bit sequence
    // in big-endian order.
    size_t acc_bits = 0;
    uint32_t acc_value = 0;

    size_t j = 0;
    for (size_t i = 0; i < in_len; i++) {
        acc_value = (acc_value << 8) | in[i];
        acc_bits += 8;

        // When we have bit_len or more bits in the accumulator, write the next
        // output element.
        if (acc_bits >= bit_len) {
            acc_bits -= bit_len;
            for (size_t x = 0; x < byte_pad; x++) {
                out[j+x] = 0;
            }
            for (size_t x = byte_pad; x < out_width; x++) {
                out[j+x] = (
                    // Big-endian
                    acc_value >> (acc_bits+(8*(out_width-x-1)))
                ) & (
                    // Apply bit_len_mask across byte boundaries
                    (bit_len_mask >> (8*(out_width-x-1))) & 0xFF
                );
            }
            j += out_width;
        }
    }
}

void CompressArray(const unsigned char* in, size_t in_len,
                   unsigned char* out, size_t out_len,