rvoip-codec-core 0.3.8

G.711 and optional G.729/Opus/AMR audio codec implementations for RVOIP
Documentation 
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//! Normative tables for the AMR-WB ISP/ISF conversions.
//!
//! From the TS 26.173 fixed-point reference (`isp_isf.tab`), which is what
//! defines the codec. Both conversions are table-and-interpolate rather than a
//! real trigonometric evaluation, so these numbers *are* the transform: a more
//! accurate cosine would give different bits and fail conformance.

/// `cos(x)` sampled at 129 points, Q15, from 0 to pi.
///
/// Indexed by the top bits of an ISF, with the low 7 bits interpolating between
/// neighbours -- which is why there are 129 entries and not 128: the last one
/// is the right-hand end of the final interval.
pub const COS_TABLE: [i16; 129] = [
    32767, 32758, 32729, 32679, 32610, 32522, 32413, 32286, 32138, 31972, 31786, 31581, 31357,
    31114, 30853, 30572, 30274, 29957, 29622, 29269, 28899, 28511, 28106, 27684, 27246, 26791,
    26320, 25833, 25330, 24812, 24279, 23732, 23170, 22595, 22006, 21403, 20788, 20160, 19520,
    18868, 18205, 17531, 16846, 16151, 15447, 14733, 14010, 13279, 12540, 11793, 11039, 10279,
    9512, 8740, 7962, 7180, 6393, 5602, 4808, 4011, 3212, 2411, 1608, 804, 0, -804, -1608, -2411,
    -3212, -4011, -4808, -5602, -6393, -7180, -7962, -8740, -9512, -10279, -11039, -11793, -12540,
    -13279, -14010, -14733, -15447, -16151, -16846, -17531, -18205, -18868, -19520, -20160, -20788,
    -21403, -22006, -22595, -23170, -23732, -24279, -24812, -25330, -25833, -26320, -26791, -27246,
    -27684, -28106, -28511, -28899, -29269, -29622, -29957, -30274, -30572, -30853, -31114, -31357,
    -31581, -31786, -31972, -32138, -32286, -32413, -32522, -32610, -32679, -32729, -32758, -32768,
];

/// Slope of `acos` over each of the 128 table intervals, Q11.
///
/// The inverse direction cannot interpolate the cosine table directly, since
/// its spacing is uneven in `x`. Each entry is the local reciprocal derivative,
/// so the search finds the interval and this converts the residual. The values
/// blow up at both ends (-26214 against -326 in the middle) because `acos` has
/// infinite slope at +/-1.
pub const ACOS_SLOPE: [i16; 128] = [
    -26214, -9039, -5243, -3799, -2979, -2405, -2064, -1771, -1579, -1409, -1279, -1170, -1079,
    -1004, -933, -880, -827, -783, -743, -708, -676, -647, -621, -599, -576, -557, -538, -521,
    -506, -492, -479, -466, -456, -445, -435, -426, -417, -410, -402, -395, -389, -383, -377, -372,
    -367, -363, -359, -355, -351, -348, -345, -342, -340, -337, -335, -333, -331, -330, -329, -328,
    -327, -326, -326, -326, -326, -326, -326, -327, -328, -329, -330, -331, -333, -335, -337, -340,
    -342, -345, -348, -351, -355, -359, -363, -367, -372, -377, -383, -389, -395, -402, -410, -417,
    -426, -435, -445, -456, -466, -479, -492, -506, -521, -538, -557, -576, -599, -621, -647, -676,
    -708, -743, -783, -827, -880, -933, -1004, -1079, -1170, -1279, -1409, -1579, -1771, -2064,
    -2405, -2979, -3799, -5243, -9039, -26214,
];