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//
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// Copyright 2010 the V8 project authors. All rights reserved.
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package jdk.nashorn.internal.runtime.doubleconv;

public class CachedPowers {

    static class CachedPower {
        final private long significand;
        final private int binaryExponent;
        final private int decimalExponent;

        CachedPower(final long significand, final int binaryExponent, final int decimalExponent) {
            this.significand = significand;
            this.binaryExponent = binaryExponent;
            this.decimalExponent = decimalExponent;
        }
    }

    static private final CachedPower[] kCachedPowers = {
            new CachedPower(0xfa8fd5a0081c0288L, -1220, -348),
            new CachedPower(0xbaaee17fa23ebf76L, -1193, -340),
            new CachedPower(0x8b16fb203055ac76L, -1166, -332),
            new CachedPower(0xcf42894a5dce35eaL, -1140, -324),
            new CachedPower(0x9a6bb0aa55653b2dL, -1113, -316),
            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)
    };

    static final int kCachedPowersOffset = 348;  // -1 * the first decimal_exponent.
    static final double kD_1_LOG2_10 = 0.30102999566398114;  //  1 / lg(10)
    // Difference between the decimal exponents in the table above.
    static final int kDecimalExponentDistance = 8;
    static final int kMinDecimalExponent = -348;
    static final int kMaxDecimalExponent = 340;

    static int getCachedPowerForBinaryExponentRange(
            final int min_exponent,
            final int max_exponent,
            final DiyFp power) {
        final int kQ = DiyFp.kSignificandSize;
        final double k = Math.ceil((min_exponent + kQ - 1) * kD_1_LOG2_10);
        final int index =
                (kCachedPowersOffset + (int) k - 1) / kDecimalExponentDistance + 1;
        assert (0 <= index && index < kCachedPowers.length);
        final CachedPower cached_power = kCachedPowers[index];
        assert (min_exponent <= cached_power.binaryExponent);
        assert (cached_power.binaryExponent <= max_exponent);
        power.setF(cached_power.significand);
        power.setE(cached_power.binaryExponent);
        return cached_power.decimalExponent;
    }


    static int getCachedPowerForDecimalExponent(final int requested_exponent,
                                                final DiyFp power) {
        assert (kMinDecimalExponent <= requested_exponent);
        assert (requested_exponent < kMaxDecimalExponent + kDecimalExponentDistance);
        final int index =
                (requested_exponent + kCachedPowersOffset) / kDecimalExponentDistance;
        final CachedPower cached_power = kCachedPowers[index];
        power.setF(cached_power.significand);
        power.setE(cached_power.binaryExponent);
        final int found_exponent = cached_power.decimalExponent;
        assert (found_exponent <= requested_exponent);
        assert (requested_exponent < found_exponent + kDecimalExponentDistance);
        return cached_power.decimalExponent;
    }

}
