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+#
+# Copyright 2005,2006,2011,2013 Free Software Foundation, Inc.
+# 
+# This file is part of GNU Radio
+# 
+# GNU Radio is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3, or (at your option)
+# any later version.
+# 
+# GNU Radio is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with GNU Radio; see the file COPYING.  If not, write to
+# the Free Software Foundation, Inc., 51 Franklin Street,
+# Boston, MA 02110-1301, USA.
+# 
+
+"""
+QAM modulation and demodulation.
+"""
+
+from math import pi, sqrt, log
+
+from gnuradio import gr
+from generic_mod_demod import generic_mod, generic_demod
+from generic_mod_demod import shared_mod_args, shared_demod_args
+from utils.gray_code import gray_code
+from utils import mod_codes
+import modulation_utils
+import digital_swig as digital
+
+# Default number of points in constellation.
+_def_constellation_points = 16
+# Whether the quadrant bits are coded differentially.
+_def_differential = True
+# Whether gray coding is used.  If differential is True then gray
+# coding is used within but not between each quadrant.
+_def_mod_code = mod_codes.NO_CODE
+
+def is_power_of_four(x):
+    v = log(x)/log(4)
+    return int(v) == v
+
+def get_bit(x, n):
+    """ Get the n'th bit of integer x (from little end)."""
+    return (x&(0x01 << n)) >> n
+
+def get_bits(x, n, k):
+    """ Get the k bits of integer x starting at bit n(from little end)."""
+    # Remove the n smallest bits
+    v = x >> n 
+    # Remove all bits bigger than n+k-1
+    return v % pow(2, k)
+
+def make_differential_constellation(m, gray_coded):
+    """
+    Create a constellation with m possible symbols where m must be
+    a power of 4.
+
+    Points are laid out in a square grid.
+
+    Bits referring to the quadrant are differentilly encoded,
+    remaining bits are gray coded.
+
+    """
+    sqrtm = pow(m, 0.5)
+    if (not isinstance(m, int) or m < 4 or not is_power_of_four(m)):
+        raise ValueError("m must be a power of 4 integer.")
+    # Each symbol holds k bits.
+    k = int(log(m) / log(2.0))
+    # First create a constellation for one quadrant containing m/4 points.
+    # The quadrant has 'side' points along each side of a quadrant.
+    side = int(sqrtm/2)
+    if gray_coded:
+        # Number rows and columns using gray codes.
+        gcs = gray_code(side)
+        # Get inverse gray codes.
+        i_gcs = dict([(v, key) for key, v in enumerate(gcs)])
+    else:
+        i_gcs = dict([(i, i) for i in range(0, side)])
+    # The distance between points is found.
+    step = 1/(side-0.5)
+
+    gc_to_x = [(i_gcs[gc]+0.5)*step for gc in range(0, side)]
+
+    # Takes the (x, y) location of the point with the quadrant along
+    # with the quadrant number. (x, y) are integers referring to which
+    # point within the quadrant it is.
+    # A complex number representing this location of this point is returned.
+    def get_c(gc_x, gc_y, quad):
+        if quad == 0:
+            return complex(gc_to_x[gc_x], gc_to_x[gc_y])
+        if quad == 1:
+            return complex(-gc_to_x[gc_y], gc_to_x[gc_x])
+        if quad == 2:
+            return complex(-gc_to_x[gc_x], -gc_to_x[gc_y])
+        if quad == 3:
+            return complex(gc_to_x[gc_y], -gc_to_x[gc_x])
+        raise StandardError("Impossible!")
+
+    # First two bits determine quadrant.
+    # Next (k-2)/2 bits determine x position.
+    # Following (k-2)/2 bits determine y position.
+    # How x and y relate to real and imag depends on quadrant (see get_c function).
+    const_map = []
+    for i in range(m):
+        y = get_bits(i, 0, (k-2)/2)
+        x = get_bits(i, (k-2)/2, (k-2)/2)
+        quad = get_bits(i, k-2, 2)
+        const_map.append(get_c(x, y, quad))
+
+    return const_map
+
+def make_non_differential_constellation(m, gray_coded):
+    side = int(pow(m, 0.5))
+    if (not isinstance(m, int) or m < 4 or not is_power_of_four(m)):
+        raise ValueError("m must be a power of 4 integer.")
+    # Each symbol holds k bits.
+    k = int(log(m) / log(2.0))
+    if gray_coded:
+        # Number rows and columns using gray codes.
+        gcs = gray_code(side)
+        # Get inverse gray codes.
+        i_gcs = mod_codes.invert_code(gcs)
+    else:
+        i_gcs = range(0, side)
+    # The distance between points is found.
+    step = 2.0/(side-1)
+
+    gc_to_x = [-1 + i_gcs[gc]*step for gc in range(0, side)]
+    # First k/2 bits determine x position.
+    # Following k/2 bits determine y position.
+    const_map = []
+    for i in range(m):
+        y = gc_to_x[get_bits(i, 0, k/2)]
+        x = gc_to_x[get_bits(i, k/2, k/2)]
+        const_map.append(complex(x,y))
+    return const_map
+
+# /////////////////////////////////////////////////////////////////////////////
+#                           QAM constellation
+# /////////////////////////////////////////////////////////////////////////////
+
+def qam_constellation(constellation_points=_def_constellation_points,
+                      differential=_def_differential,
+                      mod_code=_def_mod_code,
+                      large_ampls_to_corners=False):
+    """
+    Creates a QAM constellation object.
+
+    If large_ampls_to_corners=True then sectors that are probably
+    occupied due to a phase offset, are not mapped to the closest
+    constellation point.  Rather we take into account the fact that a
+    phase offset is probably the problem and map them to the closest
+    corner point.  It's a bit hackish but it seems to improve
+    frequency locking.
+    """
+    if mod_code == mod_codes.GRAY_CODE:
+        gray_coded = True
+    elif mod_code == mod_codes.NO_CODE:
+        gray_coded = False
+    else:
+        raise ValueError("Mod code is not implemented for QAM")
+    if differential:
+        points = make_differential_constellation(constellation_points, gray_coded=False)
+    else:
+        points = make_non_differential_constellation(constellation_points, gray_coded)
+    side = int(sqrt(constellation_points))
+    width = 2.0/(side-1)
+
+    # No pre-diff code
+    # Should add one so that we can gray-code the quadrant bits too.
+    pre_diff_code = []
+    if not large_ampls_to_corners:
+        constellation = digital.constellation_rect(points, pre_diff_code, 4,
+                                                        side, side, width, width)
+    else:
+        sector_values = large_ampls_to_corners_mapping(side, points, width)
+        constellation = digital.constellation_expl_rect(
+            points, pre_diff_code, 4, side, side, width, width, sector_values)
+
+    return constellation
+
+def find_closest_point(p, qs):
+    """
+    Return in index of the closest point in 'qs' to 'p'.
+    """
+    min_dist = None
+    min_i = None
+    for i, q in enumerate(qs):
+        dist = abs(q-p)
+        if min_dist is None or dist < min_dist:
+            min_dist = dist
+            min_i = i
+    return min_i
+
+def large_ampls_to_corners_mapping(side, points, width):
+    """
+    We have a grid that we use for decision making.  One additional row/column
+    is placed on each side of the grid.  Points in these additional rows/columns
+    are mapped to the corners rather than the closest constellation points.
+
+    Args:
+        side: The number of rows/columns in the grid that we use to do
+              decision making.
+        points: The list of constellation points.
+        width: The width of the rows/columns.
+
+    Returns:
+        sector_values maps the sector index to the constellation
+        point index.
+    """
+    # First find the indices of the corner points.
+    # Assume the corner points are the 4 points with the largest magnitudes.
+    corner_indices = []
+    corner_points = []
+    max_mag = 0
+    for i, p in enumerate(points):
+        if abs(p) > max_mag:
+            corner_indices = [i]
+            corner_points = [p]
+            max_mag = abs(p)
+        elif abs(p) == max_mag:
+            corner_indices.append(i)
+            corner_points.append(p)
+    if len(corner_indices) != 4:
+        raise ValueError("Found {0} corner indices.  Expected 4."
+                         .format(len(corner_indices)))
+    # We want an additional layer around the constellation
+    # Value in this extra layer will be mapped to the closest corner rather
+    # than the closest constellation point.
+    extra_layers = 1
+    side = side + extra_layers*2
+    # Calculate sector values
+    sector_values = []
+    for real_x in range(side):
+        for imag_x in range(side):
+            sector = real_x * side + imag_x
+            # If this sector is a normal constellation sector then
+            # use the center point.
+            c = ((real_x-side/2.0+0.5)*width +
+                 (imag_x-side/2.0+0.5)*width*1j)
+            if (real_x >= extra_layers and real_x < side-extra_layers
+                and imag_x >= extra_layers and imag_x < side-extra_layers):
+                # This is not an edge row/column.  Find closest point.
+                index = find_closest_point(c, points)
+            else:
+                # This is an edge. Find closest corner point.
+                index = corner_indices[find_closest_point(c, corner_points)]
+            sector_values.append(index)
+    return sector_values
+
+ 
+# /////////////////////////////////////////////////////////////////////////////
+#                           QAM modulator
+# /////////////////////////////////////////////////////////////////////////////
+
+class qam_mod(generic_mod):
+    """
+    Hierarchical block for RRC-filtered QAM modulation.
+    
+    The input is a byte stream (unsigned char) and the
+    output is the complex modulated signal at baseband.
+    
+    Args:
+        constellation_points: Number of constellation points (must be a power of four) (integer).
+        mod_code: Whether to use a gray_code (digital.mod_codes.GRAY_CODE) or not (digital.mod_codes.NO_CODE).
+        differential: Whether to use differential encoding (boolean).
+    """
+    # See generic_mod for additional arguments
+    __doc__ += shared_mod_args
+
+    def __init__(self, constellation_points=_def_constellation_points,
+                 differential=_def_differential,
+                 mod_code=_def_mod_code,
+                 *args, **kwargs):
+
+        """
+	Hierarchical block for RRC-filtered QAM modulation.
+
+	The input is a byte stream (unsigned char) and the
+	output is the complex modulated signal at baseband.
+
+        Args:
+            constellation_points: Number of constellation points.
+                Must be a power of 4.
+            mod_code: Specifies an encoding to use (typically used to indicated
+                      if we want gray coding, see digital.utils.mod_codes)
+
+        See generic_mod block for list of additional parameters.
+	"""
+
+        constellation = qam_constellation(constellation_points, differential,
+                                          mod_code)
+        # We take care of the gray coding in the constellation
+        # generation so it doesn't need to be done in the block.
+        super(qam_mod, self).__init__(constellation, differential=differential,
+                                      *args, **kwargs)
+
+# /////////////////////////////////////////////////////////////////////////////
+#                           QAM demodulator
+#
+# /////////////////////////////////////////////////////////////////////////////
+
+class qam_demod(generic_demod):
+    """
+    Hierarchical block for RRC-filtered QAM modulation.
+    
+    The input is a byte stream (unsigned char) and the
+    output is the complex modulated signal at baseband.
+    
+    Args:
+        constellation_points: Number of constellation points (must be a power of four) (integer).
+        mod_code: Whether to use a gray_code (digital.mod_codes.GRAY_CODE) or not (digital.mod_codes.NO_CODE).
+        differential: Whether to use differential encoding (boolean).
+    """
+    # See generic_demod for additional arguments
+    __doc__ += shared_mod_args
+
+    def __init__(self, constellation_points=_def_constellation_points,
+                 differential=_def_differential,
+                 mod_code=_def_mod_code,
+                 large_ampls_to_corner = False,
+                 *args, **kwargs):
+        """
+	Hierarchical block for RRC-filtered QAM modulation.
+
+	The input is a byte stream (unsigned char) and the
+	output is the complex modulated signal at baseband.
+
+        Args:
+            constellation_points: Number of constellation points.
+                Must be a power of 4.
+            mod_code: Specifies an encoding to use (typically used to indicated
+                      if we want gray coding, see digital.utils.mod_codes)
+            large_ampls_to_corners:  If this is set to True then when the
+                constellation is making decisions, points that are far outside
+                the constellation are mapped to the closest corner rather than
+                the closet constellation point.  This can help with phase
+                locking.
+
+        See generic_demod block for list of additional parameters.
+        """
+        constellation = qam_constellation(constellation_points, differential,
+                                          mod_code)
+        # We take care of the gray coding in the constellation
+        # generation so it doesn't need to be done in the block.
+        super(qam_demod, self).__init__(constellation, differential=differential,
+                                        *args, **kwargs)
+
+#
+# Add these to the mod/demod registry
+#
+modulation_utils.add_type_1_mod('qam', qam_mod)
+modulation_utils.add_type_1_demod('qam', qam_demod)
+modulation_utils.add_type_1_constellation('qam', qam_constellation)