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A library for invoking native functions from java
There is a newer version: 2.2.16
package jnr.ffi.provider.jffi;

import com.kenai.jffi.CallContext;
import com.kenai.jffi.CallingConvention;
import com.kenai.jffi.Platform;
import jnr.ffi.NativeType;
import jnr.ffi.Pointer;
import jnr.ffi.Struct;

import static jnr.ffi.provider.jffi.AsmUtil.isDelegate;
import static jnr.ffi.provider.jffi.CodegenUtils.ci;
import static jnr.ffi.provider.jffi.NumberUtil.sizeof;

/**
 *
 */
final class FastIntMethodGenerator extends AbstractFastNumericMethodGenerator {
    private static final boolean ENABLED = getBooleanProperty("jnr.ffi.fast-int.enabled", true);
    private static final int MAX_FASTINT_PARAMETERS = getMaximumFastIntParameters();

    private static final String[] signatures;

    private static final String[] methodNames = {
        "invokeI0", "invokeI1", "invokeI2", "invokeI3", "invokeI4", "invokeI5", "invokeI6"
    };

    static {
        signatures = new String[MAX_FASTINT_PARAMETERS + 1];
        for (int i = 0; i <= MAX_FASTINT_PARAMETERS; i++) {
            StringBuilder sb = new StringBuilder();
            sb.append('(').append(ci(CallContext.class)).append(ci(long.class));
            for (int n = 0; n < i; n++) {
                sb.append('I');
            }
            signatures[i] = sb.append(")I").toString();
        }
    }

    FastIntMethodGenerator(BufferMethodGenerator bufgen) {
        super(bufgen);
    }

    @Override
    String getInvokerMethodName(ResultType resultType, ParameterType[] parameterTypes, boolean ignoreErrno) {
        final int parameterCount = parameterTypes.length;

        if (parameterCount <= MAX_FASTINT_PARAMETERS && parameterCount <= methodNames.length) {
            return methodNames[parameterCount];

        } else {
            throw new IllegalArgumentException("invalid fast-int parameter count: " + parameterCount);
        }
    }

    @Override
    String getInvokerSignature(int parameterCount, Class nativeIntType) {
        if (parameterCount <= MAX_FASTINT_PARAMETERS && parameterCount <= signatures.length) {
            return signatures[parameterCount];
        }
        throw new IllegalArgumentException("invalid fast-int parameter count: " + parameterCount);
    }

    final Class getInvokerType() {
        return int.class;
    }

    public boolean isSupported(ResultType resultType, ParameterType[] parameterTypes, CallingConvention callingConvention) {
        final int parameterCount = parameterTypes.length;

        if (!ENABLED) {
            return false;
        }

        if (!callingConvention.equals(CallingConvention.DEFAULT) || parameterCount > MAX_FASTINT_PARAMETERS) {
            return false;
        }

        final Platform platform = Platform.getPlatform();

        if (platform.getOS().equals(Platform.OS.WINDOWS)) {
            return false;
        }

        if (!platform.getCPU().equals(Platform.CPU.I386) && !platform.getCPU().equals(Platform.CPU.X86_64)) {
            return false;
        }

        for (ParameterType parameterType : parameterTypes) {
            if (!isFastIntParameter(platform, parameterType)) {
                return false;
            }
        }

        return isFastIntResult(platform, resultType);
    }


    static int getMaximumFastIntParameters() {
        try {
            com.kenai.jffi.Invoker.class.getDeclaredMethod("invokeI6", CallContext.class, long.class,
                    int.class, int.class, int.class, int.class, int.class, int.class);
            return 6;

        } catch (Throwable t) {
            return 0;
        }
    }

    static boolean isFastIntType(Platform platform, SigType type) {
        switch (type.nativeType) {
            case SCHAR:
            case UCHAR:
            case SSHORT:
            case USHORT:
            case SINT:
            case UINT:
            case SLONG:
            case ULONG:
                return sizeof(type.nativeType) <= 4;

            default:
                return false;
        }
    }

    private static boolean isSupportedPointerParameterType(Class javaParameterType) {
        return Pointer.class.isAssignableFrom(javaParameterType)
                || Struct.class.isAssignableFrom(javaParameterType);
    }

    static boolean isFastIntResult(Platform platform, ResultType resultType) {
        return isFastIntType(platform, resultType)
                || resultType.nativeType == NativeType.VOID
                || (resultType.nativeType == NativeType.ADDRESS && sizeof(resultType)== 4)
                ;
    }


    static boolean isFastIntParameter(Platform platform, ParameterType parameterType) {
        return isFastIntType(platform, parameterType)
            || (parameterType.nativeType == NativeType.ADDRESS && sizeof(parameterType)== 4)
                && isSupportedPointerParameterType(parameterType.effectiveJavaType());
    }
}