#!/usr/bin/env python
# version 0.0.1 - http://snw.lonningdal.no/soxvolume.php
# Use constants to create list of volume coefficients with known bit length 

from decimal import Decimal

# Number of decimals to create initial coeffs for the first 6dB of atteunation
# 4 decimals   7 steps for each 6dB - step approx 1.00dB  - max length 20-bit 
# 5 decimals  16 steps for each 6dB - step approx 0.30dB  - max length 21-bit 
# 6 decimals  33 steps for each 6dB - step approx 0.14dB  - max length 22-bit 
# 7 decimals  63 steps for each 6dB - step approx 0.07dB  - max length 23-bit 
# 8 decimals 129 steps for each 6dB - step approx 0.035dB - max length 24-bit total of 2049 steps with max atteunation
nrofdecimals=8

# input as bits, 3 equals -18dB, 9 -54dB, 16 -96dB
maxattenuaton=16

# coefficients list are build in three parts, first from constant, then each 
# value are divided by a power of 2 and last we append 1.0 for zero atteunation
coeffs=list()

def build_coeffs_list(nrofdecimals, maxattenuaton):
    COEFFSCONST={4: 625, 5: 3125, 6: 15625, 7: 78125, 8: 390625}
    START={4: 10000, 5: 100000, 6: 1000000, 7: 10000000, 8: 100000000}
    MAXATTENUATION=([1, 0.5, 0.25, 0.125, 0.0625, 0.03125, 0.015625, 0.0078125, 
                     0.00390625, 0.001953125, 0.0009765625, 0.00048828125, 
                     0.000244140625, 0.0001220703125, 0.00006103515625, 
                     0.000030517578125, 0.0000152587890625])

    # from constant create first coefficients down to -6dB ~ 1-bit 
    x=START[nrofdecimals]-COEFFSCONST[nrofdecimals]
    while x >= START[nrofdecimals]/2:
        # build valid Decimal number from string and integer
        coeffs.append(Decimal('0.'+str(x))) 
        x=x-COEFFSCONST[nrofdecimals]

    # now build complete list from initial coeffs
    nrofcoeffs = len(coeffs) 
    readposition = 0
    newcoeff = 1             # must be more than 0.5

    while newcoeff >= Decimal(MAXATTENUATION[maxattenuaton-1]):
        for i in range(nrofcoeffs):        
            newcoeff=Decimal(str(coeffs[readposition])) / 2
            coeffs.append(newcoeff)
            readposition += 1
        readposition = len(coeffs) - nrofcoeffs  

    # complete the list with value for zero atteunation
    coeffs.insert(0, 1.0)  
    # END buildcoeffslist

def write_coefficients_list_to_file():
    f = open("coeffs.txt", "a")
    for coeff in coeffs:
        print (Decimal(coeff), file=f)
    f.close()

build_coeffs_list(nrofdecimals, maxattenuaton)

for coeff in coeffs:
    print (coeff)