Pack value with scale

pincfg.py

#!/usr/bin/python -tt
# -*- coding: UTF-8 -*-
# vim: ts=4 sw=4 et ai si

from __future__ import print_function

import sys
import os

import math

"""
To find the difference with original algorithm
    python pincfg.py 1000000 1 | sed -e '/Diff:/!d; /Diff: 0\//d'
where (1000000 - 1) is a maximum tested value.
"""

__author__ = "Andy Shevchenko"
__license__ = "GPL v2"

PROG = os.path.basename(sys.argv[0])

def usage():
    sys.stdout.write("Usage %s [VALUE [USE_RANGE]]\n" % PROG)

TABLE = [
    0, 1, 2, 3,
    4095, 4096, 4097,
    6141, 6144, 6147,
    8187, 8192, 8197,
    25000,
    65533, 65534, 65535, 65536, 65537,
    98323, 98324, 98325,
    253789,
    535444,
    132382720,
    135351252,
]

VMASK = 2**12 - 1
SSHIFT = 12
WIDTH = 16

def go(value, e, mask=VMASK, shift=SSHIFT, width=WIDTH):
    #
    # Original algorithm
    #
    sco = 0
    argument = value
    while argument > mask:
        argument = (argument + 1) / 2
        sco += 1
    old = argument << sco

    #
    # While-loop-less algorithm
    #
    if value >> shift:
        sc = int(math.log(value >> shift, 2)) + 1
    else:
        sc = 0

    xv1 = xv2 = value

    # Variant 1: round up
    if sc and (value & ((1 << sc) - 1)):
        xv1 += 1 << sc
    nv1 = (xv1 >> sc) << sc

    # Variant 2: closest
    if sc and (value & (1 << (sc - 1))):
        xv2 += 1 << sc
    nv2 = (xv2 >> sc) << sc

    # Initial values
    xvs = "%*d / %-*d" % (e, xv1, e, xv2)

    # Scale
    scs = "%2d%s" % (sc, sc >= width and "*" or " ")

    # New values
    nvs = "%*d / %-*d" % (e, nv1, e, nv2)

    # Difference
    d1 = abs(old - nv1)
    d2 = abs(old - nv2)
    if d1 or d2:
        ds = "Diff: %d/%-d" % (d1, d2)
    else:
        ds = ""

    print("%-*d (%s) Scale: %s Result: %s => %*d %s" % (e, value, xvs, scs, nvs, e, old, ds))

def toint(value):
    try:
        return int(value)
    except ValueError:
        usage()
        raise SystemExit("Invalid argument")

def toexp(value):
    return value and int(math.ceil(math.log(value, 10))) or 1

def main(argv):
    # Value
    value = 0
    table = True
    if len(argv) > 1:
        value = toint(argv[1])
        table = False

    # Range
    rng = 0
    if len(argv) > 2:
        rng = toint(argv[2])

    if table:
        t = iter(TABLE)
        e = toexp(max(TABLE))
    else:
        if rng:
            t = range(0, value, rng)
        else:
            t = range(value, value + 1)
        e = toexp(value)

    for value in t:
        go(value, e)

if __name__ == "__main__":
    sys.exit(main(sys.argv))