Example usage for java.math BigInteger bitLength

Introduction

In this page you can find the example usage for java.math BigInteger bitLength.

Prototype

public int bitLength() 

Source Link

Document

Returns the number of bits in the minimal two's-complement representation of this BigInteger, excluding a sign bit.

Usage

From source file:Main.java

public static BigInteger sqrt(final BigInteger val) {
    final BigInteger two = BigInteger.valueOf(2);
    BigInteger a = BigInteger.ONE.shiftLeft(val.bitLength() / 2);
    BigInteger b;//from  w  w w  .  j  a  v a2 s.c  om
    do {
        b = val.divide(a);
        a = (a.add(b)).divide(two);
    } while (a.subtract(b).abs().compareTo(two) >= 0);
    return a;
}

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From source file:com.cliqset.magicsig.util.KeyGen.java

/**
* Returns a byte-array representation of a <code>{@link BigInteger}<code>.
* No sign-bit is outputed./*from  w  ww.ja  va2s . c om*/
*
* <b>N.B.:</B> <code>{@link BigInteger}<code>'s toByteArray
* retunrs eventually longer arrays because of the leading sign-bit.
*
* @param big <code>BigInteger<code> to be converted
* @param bitlen <code>int<code> the desired length in bits of the representation
* @return a byte array with <code>bitlen</code> bits of <code>big</code>
*/
static final byte[] getBytes(BigInteger big) {
    int bitlen = big.bitLength();
    //round bitlen
    bitlen = ((bitlen + 7) >> 3) << 3;

    if (bitlen < big.bitLength()) {
        throw new IllegalArgumentException("Illegal bit len.");
    }

    byte[] bigBytes = big.toByteArray();

    if (((big.bitLength() % 8) != 0) && (((big.bitLength() / 8) + 1) == (bitlen / 8))) {
        return bigBytes;
    }

    // some copying needed
    int startSrc = 0; // no need to skip anything
    int bigLen = bigBytes.length; //valid length of the string

    if ((big.bitLength() % 8) == 0) { // correct values
        startSrc = 1; // skip sign bit

        bigLen--; // valid length of the string
    }

    int startDst = bitlen / 8 - bigLen; //pad with leading nulls
    byte[] resizedBytes = new byte[bitlen / 8];

    System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, bigLen);

    return resizedBytes;
}

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From source file:it.zero11.acme.utils.JWKUtils.java

private static byte[] toIntegerBytes(final BigInteger bigInt) {
    int bitlen = bigInt.bitLength();
    // round bitlen
    bitlen = ((bitlen + 7) >> 3) << 3;
    final byte[] bigBytes = bigInt.toByteArray();

    if (((bigInt.bitLength() % 8) != 0) && (((bigInt.bitLength() / 8) + 1) == (bitlen / 8))) {
        return bigBytes;
    }/*  w w w. j  a  va2 s .com*/
    // set up params for copying everything but sign bit
    int startSrc = 0;
    int len = bigBytes.length;

    // if bigInt is exactly byte-aligned, just skip signbit in copy
    if ((bigInt.bitLength() % 8) == 0) {
        startSrc = 1;
        len--;
    }
    final int startDst = bitlen / 8 - len; // to pad w/ nulls as per spec
    final byte[] resizedBytes = new byte[bitlen / 8];
    System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, len);
    return resizedBytes;
}

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From source file:Main.java

public static byte[] generateJSF(BigInteger g, BigInteger h) {
    int digits = Math.max(g.bitLength(), h.bitLength()) + 1;
    byte[] jsf = new byte[digits];

    BigInteger k0 = g, k1 = h;//from w w w.j a  v a2  s  .c  om
    int j = 0, d0 = 0, d1 = 0;

    while (k0.signum() > 0 || k1.signum() > 0 || d0 > 0 || d1 > 0) {
        int n0 = (k0.intValue() + d0) & 7, n1 = (k1.intValue() + d1) & 7;

        int u0 = n0 & 1;
        if (u0 != 0) {
            u0 -= (n0 & 2);
            if ((n0 + u0) == 4 && (n1 & 3) == 2) {
                u0 = -u0;
            }
        }

        int u1 = n1 & 1;
        if (u1 != 0) {
            u1 -= (n1 & 2);
            if ((n1 + u1) == 4 && (n0 & 3) == 2) {
                u1 = -u1;
            }
        }

        if ((d0 << 1) == 1 + u0) {
            d0 = 1 - d0;
        }
        if ((d1 << 1) == 1 + u1) {
            d1 = 1 - d1;
        }

        k0 = k0.shiftRight(1);
        k1 = k1.shiftRight(1);

        jsf[j++] = (byte) ((u0 << 4) | (u1 & 0xF));
    }

    // Reduce the JSF array to its actual length
    if (jsf.length > j) {
        jsf = trim(jsf, j);
    }

    return jsf;
}

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From source file:Main.java

public static int[] generateCompactNaf(BigInteger k) {
    if ((k.bitLength() >>> 16) != 0) {
        throw new IllegalArgumentException("'k' must have bitlength < 2^16");
    }//from   w w w.  jav a 2 s.co m
    if (k.signum() == 0) {
        return EMPTY_INTS;
    }

    BigInteger _3k = k.shiftLeft(1).add(k);

    int bits = _3k.bitLength();
    int[] naf = new int[bits >> 1];

    BigInteger diff = _3k.xor(k);

    int highBit = bits - 1, length = 0, zeroes = 0;
    for (int i = 1; i < highBit; ++i) {
        if (!diff.testBit(i)) {
            ++zeroes;
            continue;
        }

        int digit = k.testBit(i) ? -1 : 1;
        naf[length++] = (digit << 16) | zeroes;
        zeroes = 1;
        ++i;
    }

    naf[length++] = (1 << 16) | zeroes;

    if (naf.length > length) {
        naf = trim(naf, length);
    }

    return naf;
}

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From source file:Main.java

public static byte[] generateJSF(BigInteger g, BigInteger h) {
    int digits = Math.max(g.bitLength(), h.bitLength()) + 1;
    byte[] jsf = new byte[digits];

    BigInteger k0 = g, k1 = h;// ww w.  j  a v  a 2  s.  co  m
    int j = 0, d0 = 0, d1 = 0;

    int offset = 0;
    while ((d0 | d1) != 0 || k0.bitLength() > offset || k1.bitLength() > offset) {
        int n0 = ((k0.intValue() >>> offset) + d0) & 7, n1 = ((k1.intValue() >>> offset) + d1) & 7;

        int u0 = n0 & 1;
        if (u0 != 0) {
            u0 -= (n0 & 2);
            if ((n0 + u0) == 4 && (n1 & 3) == 2) {
                u0 = -u0;
            }
        }

        int u1 = n1 & 1;
        if (u1 != 0) {
            u1 -= (n1 & 2);
            if ((n1 + u1) == 4 && (n0 & 3) == 2) {
                u1 = -u1;
            }
        }

        if ((d0 << 1) == 1 + u0) {
            d0 ^= 1;
        }
        if ((d1 << 1) == 1 + u1) {
            d1 ^= 1;
        }

        if (++offset == 30) {
            offset = 0;
            k0 = k0.shiftRight(30);
            k1 = k1.shiftRight(30);
        }

        jsf[j++] = (byte) ((u0 << 4) | (u1 & 0xF));
    }

    // Reduce the JSF array to its actual length
    if (jsf.length > j) {
        jsf = trim(jsf, j);
    }

    return jsf;
}

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From source file:Main.java

public static byte[] generateJSF(BigInteger g, BigInteger h) {
    byte[] jsf = new byte[(Math.max(g.bitLength(), h.bitLength()) + 1)];
    BigInteger k0 = g;//from  w  w w .j ava2 s . co  m
    BigInteger k1 = h;
    int d0 = 0;
    int d1 = 0;
    int offset = 0;
    int j = 0;
    while (true) {
        if ((d0 | d1) == 0 && k0.bitLength() <= offset && k1.bitLength() <= offset) {
            break;
        }
        int n0 = ((k0.intValue() >>> offset) + d0) & 7;
        int n1 = ((k1.intValue() >>> offset) + d1) & 7;
        int u0 = n0 & 1;
        if (u0 != 0) {
            u0 -= n0 & 2;
            if (n0 + u0 == 4 && (n1 & 3) == 2) {
                u0 = -u0;
            }
        }
        int u1 = n1 & 1;
        if (u1 != 0) {
            u1 -= n1 & 2;
            if (n1 + u1 == 4 && (n0 & 3) == 2) {
                u1 = -u1;
            }
        }
        if ((d0 << 1) == u0 + 1) {
            d0 ^= 1;
        }
        if ((d1 << 1) == u1 + 1) {
            d1 ^= 1;
        }
        offset++;
        if (offset == 30) {
            offset = 0;
            k0 = k0.shiftRight(30);
            k1 = k1.shiftRight(30);
        }
        int j2 = j + 1;
        jsf[j] = (byte) ((u0 << 4) | (u1 & 15));
        j = j2;
    }
    if (jsf.length > j) {
        return trim(jsf, j);
    }
    return jsf;
}

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From source file:org.keycloak.jose.jwk.JWKBuilder.java

/**
 * Copied from org.apache.commons.codec.binary.Base64
 *//*from  w w w .j av  a 2  s . co  m*/
private static byte[] toIntegerBytes(final BigInteger bigInt) {
    int bitlen = bigInt.bitLength();
    // round bitlen
    bitlen = ((bitlen + 7) >> 3) << 3;
    final byte[] bigBytes = bigInt.toByteArray();

    if (((bigInt.bitLength() % 8) != 0) && (((bigInt.bitLength() / 8) + 1) == (bitlen / 8))) {
        return bigBytes;
    }
    // set up params for copying everything but sign bit
    int startSrc = 0;
    int len = bigBytes.length;

    // if bigInt is exactly byte-aligned, just skip signbit in copy
    if ((bigInt.bitLength() % 8) == 0) {
        startSrc = 1;
        len--;
    }
    final int startDst = bitlen / 8 - len; // to pad w/ nulls as per spec
    final byte[] resizedBytes = new byte[bitlen / 8];
    System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, len);
    return resizedBytes;
}

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From source file:Main.java

/**
 * Compute the square root of x to a given scale, x >= 0. Use Newton's
 * algorithm./*from  w w  w.  j av a 2  s .com*/
 * 
 * @param x
 *            the value of x
 * @return the result value
 */
public static BigDecimal sqrt(BigDecimal x) {
    // Check that x >= 0.
    if (x.signum() < 0) {
        throw new ArithmeticException("x < 0");
    }

    // n = x*(10^(2*SCALE))
    BigInteger n = x.movePointRight(SCALE << 1).toBigInteger();

    // The first approximation is the upper half of n.
    int bits = (n.bitLength() + 1) >> 1;
    BigInteger ix = n.shiftRight(bits);
    BigInteger ixPrev;

    // Loop until the approximations converge
    // (two successive approximations are equal after rounding).
    do {
        ixPrev = ix;

        // x = (x + n/x)/2
        ix = ix.add(n.divide(ix)).shiftRight(1);

        Thread.yield();
    } while (ix.compareTo(ixPrev) != 0);

    return new BigDecimal(ix, SCALE);
}

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From source file:cc.redberry.core.number.NumberUtils.java

/**
 * Computes the integer square root of a number.
 *
 * @param n The number./* ww  w.  j a v  a  2 s.  c  o  m*/
 * @return The integer square root, i.e. the largest number whose square
 *         doesn't exceed n.
 */
public static BigInteger sqrt(BigInteger n) {
    if (n.signum() >= 0) {
        final int bitLength = n.bitLength();
        BigInteger root = BigInteger.ONE.shiftLeft(bitLength / 2);

        while (!isSqrtXXX(n, root))
            root = root.add(n.divide(root)).divide(TWO);
        return root;
    } else
        throw new ArithmeticException("square root of negative number");
}

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