sebastienros.jint/Jint/Native/Number/Dtoa/CachePowers.cs

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// Ported to Java from Mozilla's version of V8-dtoa by Hannes Wallnoefer.
// The original revision was 67d1049b0bf9 from the mozilla-central tree.

using System.Diagnostics;

namespace Jint.Native.Number.Dtoa
{

    public class CachedPowers
    {
        private const double Kd1Log210 = 0.30102999566398114; //  1 / lg(10)

        private class CachedPower
        {
            internal readonly long Significand;
            internal readonly short BinaryExponent;
            internal readonly short DecimalExponent;

            internal CachedPower(ulong significand, short binaryExponent, short decimalExponent)
            {
                Significand = (long) significand;
                BinaryExponent = binaryExponent;
                DecimalExponent = decimalExponent;
            }
        }


        internal static int GetCachedPower(int e, int alpha, int gamma, DiyFp cMk)
        {
            const int kQ = DiyFp.KSignificandSize;
            double k = System.Math.Ceiling((alpha - e + kQ - 1)*Kd1Log210);
            int index = (GrisuCacheOffset + (int) k - 1)/CachedPowersSpacing + 1;
            CachedPower cachedPower = CACHED_POWERS[index];

            cMk.F = cachedPower.Significand;
            cMk.E = cachedPower.BinaryExponent;
            Debug.Assert((alpha <= cMk.E + e) && (cMk.E + e <= gamma));
            return cachedPower.DecimalExponent;
        }

        // Code below is converted from GRISU_CACHE_NAME(8) in file "powers-ten.h"
        // Regexp to convert this from original C++ source:
        // \{GRISU_UINT64_C\((\w+), (\w+)\), (\-?\d+), (\-?\d+)\}

        // interval between entries  of the powers cache below
        private const int CachedPowersSpacing = 8;

        private static readonly CachedPower[] CACHED_POWERS =
        {
            new CachedPower(0xe61acf033d1a45dfL, -1087, -308),
            new CachedPower(0xab70fe17c79ac6caL, -1060, -300),
            new CachedPower(0xff77b1fcbebcdc4fL, -1034, -292),
            new CachedPower(0xbe5691ef416bd60cL, -1007, -284),
            new CachedPower(0x8dd01fad907ffc3cL, -980, -276),
            new CachedPower(0xd3515c2831559a83L, -954, -268),
            new CachedPower(0x9d71ac8fada6c9b5L, -927, -260),
            new CachedPower(0xea9c227723ee8bcbL, -901, -252),
            new CachedPower(0xaecc49914078536dL, -874, -244),
            new CachedPower(0x823c12795db6ce57L, -847, -236),
            new CachedPower(0xc21094364dfb5637L, -821, -228),
            new CachedPower(0x9096ea6f3848984fL, -794, -220),
            new CachedPower(0xd77485cb25823ac7L, -768, -212),
            new CachedPower(0xa086cfcd97bf97f4L, -741, -204),
            new CachedPower(0xef340a98172aace5L, -715, -196),
            new CachedPower(0xb23867fb2a35b28eL, -688, -188),
            new CachedPower(0x84c8d4dfd2c63f3bL, -661, -180),
            new CachedPower(0xc5dd44271ad3cdbaL, -635, -172),
            new CachedPower(0x936b9fcebb25c996L, -608, -164),
            new CachedPower(0xdbac6c247d62a584L, -582, -156),
            new CachedPower(0xa3ab66580d5fdaf6L, -555, -148),
            new CachedPower(0xf3e2f893dec3f126L, -529, -140),
            new CachedPower(0xb5b5ada8aaff80b8L, -502, -132),
            new CachedPower(0x87625f056c7c4a8bL, -475, -124),
            new CachedPower(0xc9bcff6034c13053L, -449, -116),
            new CachedPower(0x964e858c91ba2655L, -422, -108),
            new CachedPower(0xdff9772470297ebdL, -396, -100),
            new CachedPower(0xa6dfbd9fb8e5b88fL, -369, -92),
            new CachedPower(0xf8a95fcf88747d94L, -343, -84),
            new CachedPower(0xb94470938fa89bcfL, -316, -76),
            new CachedPower(0x8a08f0f8bf0f156bL, -289, -68),
            new CachedPower(0xcdb02555653131b6L, -263, -60),
            new CachedPower(0x993fe2c6d07b7facL, -236, -52),
            new CachedPower(0xe45c10c42a2b3b06L, -210, -44),
            new CachedPower(0xaa242499697392d3L, -183, -36),
            new CachedPower(0xfd87b5f28300ca0eL, -157, -28),
            new CachedPower(0xbce5086492111aebL, -130, -20),
            new CachedPower(0x8cbccc096f5088ccL, -103, -12),
            new CachedPower(0xd1b71758e219652cL, -77, -4),
            new CachedPower(0x9c40000000000000L, -50, 4),
            new CachedPower(0xe8d4a51000000000L, -24, 12),
            new CachedPower(0xad78ebc5ac620000L, 3, 20),
            new CachedPower(0x813f3978f8940984L, 30, 28),
            new CachedPower(0xc097ce7bc90715b3L, 56, 36),
            new CachedPower(0x8f7e32ce7bea5c70L, 83, 44),
            new CachedPower(0xd5d238a4abe98068L, 109, 52),
            new CachedPower(0x9f4f2726179a2245L, 136, 60),
            new CachedPower(0xed63a231d4c4fb27L, 162, 68),
            new CachedPower(0xb0de65388cc8ada8L, 189, 76),
            new CachedPower(0x83c7088e1aab65dbL, 216, 84),
            new CachedPower(0xc45d1df942711d9aL, 242, 92),
            new CachedPower(0x924d692ca61be758L, 269, 100),
            new CachedPower(0xda01ee641a708deaL, 295, 108),
            new CachedPower(0xa26da3999aef774aL, 322, 116),
            new CachedPower(0xf209787bb47d6b85L, 348, 124),
            new CachedPower(0xb454e4a179dd1877L, 375, 132),
            new CachedPower(0x865b86925b9bc5c2L, 402, 140),
            new CachedPower(0xc83553c5c8965d3dL, 428, 148),
            new CachedPower(0x952ab45cfa97a0b3L, 455, 156),
            new CachedPower(0xde469fbd99a05fe3L, 481, 164),
            new CachedPower(0xa59bc234db398c25L, 508, 172),
            new CachedPower(0xf6c69a72a3989f5cL, 534, 180),
            new CachedPower(0xb7dcbf5354e9beceL, 561, 188),
            new CachedPower(0x88fcf317f22241e2L, 588, 196),
            new CachedPower(0xcc20ce9bd35c78a5L, 614, 204),
            new CachedPower(0x98165af37b2153dfL, 641, 212),
            new CachedPower(0xe2a0b5dc971f303aL, 667, 220),
            new CachedPower(0xa8d9d1535ce3b396L, 694, 228),
            new CachedPower(0xfb9b7cd9a4a7443cL, 720, 236),
            new CachedPower(0xbb764c4ca7a44410L, 747, 244),
            new CachedPower(0x8bab8eefb6409c1aL, 774, 252),
            new CachedPower(0xd01fef10a657842cL, 800, 260),
            new CachedPower(0x9b10a4e5e9913129L, 827, 268),
            new CachedPower(0xe7109bfba19c0c9dL, 853, 276),
            new CachedPower(0xac2820d9623bf429L, 880, 284),
            new CachedPower(0x80444b5e7aa7cf85L, 907, 292),
            new CachedPower(0xbf21e44003acdd2dL, 933, 300),
            new CachedPower(0x8e679c2f5e44ff8fL, 960, 308),
            new CachedPower(0xd433179d9c8cb841L, 986, 316),
            new CachedPower(0x9e19db92b4e31ba9L, 1013, 324),
            new CachedPower(0xeb96bf6ebadf77d9L, 1039, 332),
            new CachedPower(0xaf87023b9bf0ee6bL, 1066, 340)
        };

        private const int GrisuCacheOffset = 308;


    }
}