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dbrochart |
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#### ####
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#### distances.py ####
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#### ####
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#### This file is part of the turbo decoder IP core project ####
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#### http://www.opencores.org/projects/turbocodes/ ####
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#### ####
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#### Author(s): ####
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#### - David Brochart(dbrochart@opencores.org) ####
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#### ####
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#### All additional information is available in the README.txt ####
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#### file. ####
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#### ####
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######################################################################
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#### ####
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#### Copyright (C) 2005 Authors ####
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#### ####
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#### This source file may be used and distributed without ####
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#### restriction provided that this copyright statement is not ####
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#### removed from the file and that any derivative work contains ####
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#### the original copyright notice and the associated disclaimer. ####
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#### ####
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#### This source file is free software; you can redistribute it ####
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#### and/or modify it under the terms of the GNU Lesser General ####
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#### Public License as published by the Free Software Foundation; ####
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#### either version 2.1 of the License, or (at your option) any ####
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#### later version. ####
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#### ####
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#### This source is distributed in the hope that it will be ####
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#### useful, but WITHOUT ANY WARRANTY; without even the implied ####
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#### warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ####
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#### PURPOSE. See the GNU Lesser General Public License for more ####
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#### details. ####
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#### ####
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#### You should have received a copy of the GNU Lesser General ####
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#### Public License along with this source; if not, download it ####
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#### from http://www.opencores.org/lgpl.shtml ####
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#### ####
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######################################################################
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from misc import opposite, adder, register
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from myhdl import Signal, intbv, always_comb, instance
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def partDistance(a, b, y1, y2, res, ref = intbv(0, 0, 8)):
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""" Partial distance from (a, b, y1, y2) = ref.
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ref -- reference to compute the distance from
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a, b, y1, y2 -- in : decoder input signals, coded with n bits
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res -- out : partial distance signal, coded with (n + 2) bits
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"""
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@instance
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def partDistanceLogic():
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while 1:
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if ref[2] == 0:
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bSigned = b.val
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else:
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bSigned = -b.val
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if ref[1] == 0:
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y1Signed = y1.val
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else:
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y1Signed = -y1.val
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if ref[0] == 0:
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y2Signed = y2.val
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else:
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y2Signed = -y2.val
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res.next = a.val + bSigned + y1Signed + y2Signed
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yield a, b, y1, y2
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return partDistanceLogic
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def distance(partDist, z, dist, n = 4):
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""" Distance computation.
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n -- number of bits for the coding of the decoder input signals
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partDist -- in : sum of the decoder input signals
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z -- in : extrinsic information
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dist -- out : distance
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"""
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@always_comb
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def distanceLogic():
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dist.next = (4 * (2 ** (n - 1) - 1) + partDist.val) / 2 + z.val
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return distanceLogic
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def distances(a, b, y1, y2, z, distance16, n = 4):
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""" Computes the 16 distances from the decoder input signals.
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n -- number of bits for the coding of the decoder input signals
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a, b, y1, y2 -- in : decoder input signals, coded with n bits
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z -- in : extrinsic information signals (x4), coded with m bits
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distance16 -- out : distance signals (x16)
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"""
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partDist = [Signal(intbv(0, -(2**(n+1)), 2**(n+1))) for i in range(16)]
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opposite_i = [None for i in range(8)]
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distance_i = [None for i in range(16)]
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partDistance_i = [None for i in range(8)]
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for i in range(8):
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partDistance_i[i] = partDistance(a, b, y1, y2, partDist[i], intbv(i, 0, 8))
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for i in range(8):
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opposite_i[i] = opposite(partDist[i], partDist[15 - i])
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for i in range(16):
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distance_i[i] = distance(partDist[i], z[i / 4], distance16[i], n)
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return partDistance_i, opposite_i, distance_i
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def reduction(org, chd, q = 8):
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""" (Reduction: if anyone's q(th) bit is set, divide everyone by 2.)
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Temporary test: when everyone's q(th) bit is set, reset everyone's q(th) bit.
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q -- accumulated distance width
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org -- in : original array of 8 q-bit accumulated distances
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chd -- out : reduced array of 8 q-bit accumulated distances
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"""
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# tmp = intbv(0, 0, 2**q)
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@instance
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def reductionLogic():
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while 1:
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# msb = bool(0)
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msb = bool(1)
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for i in range(8):
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# msb = msb or org[i].val[q-1]
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msb = msb and org[i].val[q - 1]
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for i in range(8):
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chd[i].next[q-1:0] = org[i].val[q-1:0]
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chd[i].next[q - 1] = (not msb) and org[i].val[q - 1]
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# if msb == 1:
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# tmp[q-1:0] = org[i].val[q:1]
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# else:
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# tmp = org[i].val
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# chd[i].next = tmp
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yield org[0], org[1], org[2], org[3], org[4], org[5], org[6], org[7]
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return reductionLogic
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def accDist(clk, rst, accDistReg, dist, accDistNew, q = 8):
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""" Accumulated distances.
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q -- in : accumulated distance width
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clk, rst -- in : clock and negative reset
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accDistReg -- in : original array of 8 q-bit accumulated distance registers
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dist -- in : array of 16 distances
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accDistNew -- out : array of 32 (q+1)-bit accumulated distances
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"""
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adder_i = [None for i in range(32)]
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register_i = [None for i in range(8)]
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accDistOld = [Signal(intbv(0, 0, 2**q)) for i in range(8)]
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accDistRed = [Signal(intbv(0, 0, 2**q)) for i in range(8)]
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accDistRegSorted = [Signal(intbv(0, 0, 2**q)) for i in range(8)]
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accDistRegDelta = [Signal(intbv(0, 0, 2**q)) for i in range(8)]
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distIndex = [0, 7, 11, 12, 0, 7, 11, 12, 2, 5, 9, 14, 2, 5, 9, 14, 3, 4, 8, 15, 3, 4, 8, 15, 1, 6, 10, 13, 1, 6, 10, 13]
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for i in range(32):
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adder_i[i] = adder(accDistOld[i/4], dist[distIndex[i]], accDistNew[i])
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reduction_i0 = reduction(accDistReg, accDistRed, q)
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for i in range(8):
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register_i[i] = register(clk, rst, accDistRed[i], accDistOld[i])
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return adder_i, register_i, reduction_i0
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