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Spongy Castle is a package-rename (org.bouncycastle.* to org.spongycastle.*) of Bouncy Castle intended for the Android platform. Android unfortunately ships with a stripped-down version of Bouncy Castle, which prevents easy upgrades - Spongy Castle overcomes this and provides a full, up-to-date version of the Bouncy Castle cryptographic libs.

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package org.spongycastle.asn1.x9;

import java.math.BigInteger;

import org.spongycastle.math.ec.ECCurve;
import org.spongycastle.math.ec.ECFieldElement;

public class X9IntegerConverter
{
    public int getByteLength(
        ECCurve c)
    {
        return (c.getFieldSize() + 7) / 8;
    }

    public int getByteLength(
        ECFieldElement fe)
    {
        return (fe.getFieldSize() + 7) / 8;
    }

    public byte[] integerToBytes(
        BigInteger s,
        int        qLength)
    {
        byte[] bytes = s.toByteArray();
        
        if (qLength < bytes.length)
        {
            byte[] tmp = new byte[qLength];
        
            System.arraycopy(bytes, bytes.length - tmp.length, tmp, 0, tmp.length);
            
            return tmp;
        }
        else if (qLength > bytes.length)
        {
            byte[] tmp = new byte[qLength];
        
            System.arraycopy(bytes, 0, tmp, tmp.length - bytes.length, bytes.length);
            
            return tmp; 
        }
    
        return bytes;
    }
}