def get_log2_expansion()

in rtl/log/luts/gen_tables.py [0:0]

• 23 lines of code
• 8 McCabe index (conditional complexity)

def get_log2_expansion(i, in_bits, out_bits, enable_rounding=True):
    prec_bits = out_bits * 4
    fam20 = FixedPoint.FXfamily(prec_bits)

    x = (FixedPoint.FXnum(i, fam20) / (2 ** in_bits))
    orig_str = x.toBinaryString()[2:2+in_bits]
    x = (x + 1).log() / math.log(2)
    pow2_str = x.toBinaryString()

    keep_bit = pow2_str[2+out_bits-1] == '1'
    guard_bit = pow2_str[2+out_bits] == '1'
    round_bit = pow2_str[2+out_bits+1] == '1'
    sticky_bits = pow2_str[2+out_bits+2:].find('1') != -1

    round_down = (not guard_bit) or ((not keep_bit) and guard_bit and (not round_bit) and (not sticky_bits))

    if (not round_down and enable_rounding):
        add = FixedPoint.FXnum(1, fam20) >> out_bits
        x = x + add

    before_round = pow2_str[2:2+out_bits]
    after_round = x.toBinaryString()[2:2+out_bits]

    is_overlap = False

    if after_round in overlaps:
        is_overlap = True
    else:
        overlaps[after_round] = True

    return orig_str, before_round, after_round, not round_down, is_overlap