com.github.mathiewz.slick.ibxm.LogTable Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of modernized-slick Show documentation
The main purpose of this libraryis to modernize and maintain the slick2D library.
The newest version!

package com.github.mathiewz.slick.ibxm;

/*
 * Base-2 Log and Exp functions, using linear-interpolated tables.
 */
public class LogTable {
    private static final int TABLE_SHIFT = 7; // 128 points (+1 for interp)
    private static final int INTERP_SHIFT = IBXM.FP_SHIFT - TABLE_SHIFT;
    private static final int INTERP_MASK = (1 << INTERP_SHIFT) - 1;

    private static final int[] exp_2_table = { 32768, 32945, 33124, 33304, 33485, 33667, 33850, 34033, 34218, 34404, 34591, 34779, 34968, 35157, 35348, 35540, 35733, 35927, 36122, 36319, 36516, 36714, 36913, 37114, 37315, 37518, 37722, 37926, 38132, 38339, 38548, 38757, 38967, 39179, 39392, 39606, 39821, 40037, 40254, 40473, 40693, 40914, 41136, 41359, 41584, 41810, 42037, 42265, 42494, 42725, 42957, 43190, 43425, 43661, 43898, 44136, 44376, 44617, 44859, 45103, 45347, 45594, 45841, 46090, 46340, 46592, 46845, 47099, 47355, 47612, 47871, 48131, 48392, 48655, 48919, 49185, 49452, 49720, 49990, 50262, 50535, 50809, 51085, 51362, 51641, 51922, 52204, 52487, 52772, 53059, 53347, 53636, 53928, 54220, 54515, 54811, 55108, 55408, 55709, 56011, 56315, 56621, 56928, 57238, 57548, 57861, 58175, 58491, 58809, 59128, 59449, 59772, 60096, 60423, 60751, 61081, 61412, 61746, 62081, 62418, 62757, 63098, 63440, 63785, 64131, 64479, 64830, 65182, 65536 };

    private static final int[] log_2_table = { 0, 367, 732, 1095, 1454, 1811, 2165, 2517, 2865, 3212, 3556, 3897, 4236, 4572, 4906, 5238, 5568, 5895, 6220, 6542, 6863, 7181, 7497, 7812, 8124, 8434, 8742, 9048, 9352, 9654, 9954, 10252, 10548, 10843, 11136, 11427, 11716, 12003, 12289, 12573, 12855, 13136, 13414, 13692, 13967, 14241, 14514, 14785, 15054, 15322, 15588, 15853, 16117, 16378, 16639, 16898, 17156, 17412, 17667, 17920, 18172, 18423, 18673, 18921, 19168, 19413, 19657, 19900, 20142, 20383, 20622, 20860, 21097, 21333, 21568, 21801, 22034, 22265, 22495, 22724, 22952, 23178, 23404, 23628, 23852, 24074, 24296, 24516, 24736, 24954, 25171, 25388, 25603, 25817, 26031, 26243, 26455, 26665, 26875, 27084, 27292, 27499, 27705, 27910, 28114, 28317, 28520, 28721, 28922, 29122, 29321, 29519, 29716, 29913, 30109, 30304, 30498, 30691, 30884, 31076, 31267, 31457, 31646, 31835, 32023, 32210, 32397, 32582, 32768 };

    /*
     * Calculate log-base-2 of x (non-fixed-point).
     * A fixed point value is returned.
     */
    public static int log2(int x) {
        int shift;
        /* Scale x to range 1.0 <= x < 2.0 */
        shift = IBXM.FP_SHIFT;
        while (x < IBXM.FP_ONE) {
            x <<= 1;
            shift--;
        }
        while (x >= IBXM.FP_ONE << 1) {
            x >>= 1;
            shift++;
        }
        return IBXM.FP_ONE * shift + evalTable(log_2_table, x - IBXM.FP_ONE);
    }

    /*
     * Raise 2 to the power x (fixed point).
     * A fixed point value is returned.
     */
    public static int raise2(int x) {
        int y;
        y = evalTable(exp_2_table, x & IBXM.FP_MASK) << IBXM.FP_SHIFT;
        return y >> IBXM.FP_SHIFT - (x >> IBXM.FP_SHIFT);
    }

    private static int evalTable(int[] table, int x) {
        int tableIdx = x >> INTERP_SHIFT;
        int c = table[tableIdx];
        int m = table[tableIdx + 1] - c;
        int y = (m * (x & INTERP_MASK) >> INTERP_SHIFT) + c;
        return y >> 15 - IBXM.FP_SHIFT;
    }
}