ConcordeLib.kt

package me.hanslovsky.konkorde

import com.sun.jna.Library
import com.sun.jna.Memory
import com.sun.jna.Native
import com.sun.jna.Pointer
import com.sun.jna.Structure

interface ConcordeLib  : Library {

	fun CCutil_sprand(seed: Int, rstate: CCrandstate): Unit

	companion object {
		@JvmStatic val INSTANCE = Native.load("concorde", ConcordeLib::class.java)

	}

	@Structure.FieldOrder("a", "b", "arr")
	open class CCrandstate : Structure() {
		class ByReference : CCrandstate(), Structure.ByReference
		@JvmField var a: Int = 0
		@JvmField var b: Int = 0
		@JvmField val arr: Pointer = Memory(55L * Native.getNativeSize(Integer.TYPE))

		override fun toString(): String {
			return "${this::class.java}(a=$a, b=$b, arr=${arr})"
		}
	}

}
fun main() {
	val rstate = ConcordeLib.CCrandstate()
	println("before: rstate=$rstate rstate.arr[0]=${rstate.arr.getInt(0)}")
	// before: rstate=class me.hanslovsky.konkorde.ConcordeLib$CCrandstate(a=0, b=0, arr=allocated@0x7f25a46eefc0 (220 bytes)) rstate.arr[0]=-1543503728
	ConcordeLib.INSTANCE.CCutil_sprand(0, rstate)
	// rstate.arr pointer address changes after native call
	// even though CCutil_sprand does not allocate any memory
	println("after:  rstate=$rstate")
	//after:  rstate=class me.hanslovsky.konkorde.ConcordeLib$CCrandstate(a=0, b=24, arr=native@0x1b3928f93272b759)
	// next line will fail with SIGSEGV
	println("after:  rstate=$rstate rstate.arr[0]=${rstate.arr.getInt(0)}")
	//#
	//# A fatal error has been detected by the Java Runtime Environment:
	//#
	//#  SIGSEGV (0xb) at pc=0x00007f256dc09e18, pid=48562, tid=48563
}

ConcordeLibFixed.kt

package me.hanslovsky.konkorde

import com.sun.jna.Library
import com.sun.jna.Native
import com.sun.jna.Structure

interface ConcordeLibFixed  : Library {

	fun CCutil_sprand(seed: Int, rstate: CCrandstate): Unit

	companion object {
		@JvmStatic val INSTANCE = Native.load("concorde", ConcordeLibFixed::class.java)

	}

	@Structure.FieldOrder("a", "b", "arr")
open class CCrandstate : Structure() {
	class ByReference : CCrandstate(), Structure.ByReference
	@JvmField var a: Int = 0
	@JvmField var b: Int = 0
	@JvmField val arr: IntArray = IntArray(55) // Memory(55L * Native.getNativeSize(Integer.TYPE))

	override fun toString(): String {
		return "${this::class.java}(a=$a, b=$b, arr=${arr})"
	}
}

}
fun main() {
	val rstate = ConcordeLibFixed.CCrandstate()
	println("before: rstate=$rstate rstate.arr[0]=${rstate.arr.get(0)}")
	// before: rstate=class me.hanslovsky.konkorde.ConcordeLib$CCrandstate(a=0, b=0, arr=allocated@0x7f25a46eefc0 (220 bytes)) rstate.arr[0]=-1543503728
	ConcordeLibFixed.INSTANCE.CCutil_sprand(0, rstate)
	// rstate.arr pointer address changes after native call
	// even though CCutil_sprand does not allocate any memory
	println("after:  rstate=$rstate")
	//after:  rstate=class me.hanslovsky.konkorde.ConcordeLib$CCrandstate(a=0, b=24, arr=native@0x1b3928f93272b759)
	println("after:  rstate=$rstate rstate.arr[0]=${rstate.arr.get(0)}")
}

ConcordeLibPointer.kt

package me.hanslovsky.konkorde

import com.sun.jna.Library
import com.sun.jna.Native
import com.sun.jna.Pointer

interface ConcordeLibPointer : Library {

	fun CCutil_sprand(seed: Int, rstate: Pointer): Unit

	companion object {
		@JvmStatic val INSTANCE = Native.load("concorde", ConcordeLibPointer::class.java)
	}

	class CCRandStatePointer : Pointer(allocate()) {

		val a: Int get() = getInt(0)
		val b: Int get() = getInt(4)
		val arr = { index: Int -> getInt(8L + 4*index) }

		override fun toString() = "p($a, $b, ${arr(0)})"

		companion object {
			private fun allocate() = Native.malloc(4*(1 + 1 + 55))
		}
	}

}
fun main() {
	val rstate = ConcordeLibPointer.CCRandStatePointer()
	println("before: rstate=$rstate")
	// before: rstate=p(-738197360, 32515, -738197360)
	ConcordeLibPointer.INSTANCE.CCutil_sprand(0, rstate)
	println("after:  rstate=$rstate")
	//after:  rstate=p(0, 24, 846378841)
}

relevant_c_code.c

#include "machdefs.h"
#include "util.h"

typedef struct CCrandstate {
    int a;
    int b;
    int arr[55];
} CCrandstate;

void CCutil_sprand (int seed, CCrandstate *r)
{
    int i, ii;
    int last, next;
    int *arr = r->arr;

    seed %= CC_PRANDMAX;
    if (seed < 0) seed += CC_PRANDMAX;

    arr[0] = last = seed;
    next = 1;
    for (i = 1; i < 55; i++) {
        ii = (21 * i) % 55;
        arr[ii] = next;
        next = last - next;
        if (next < 0)
            next += CC_PRANDMAX;
        last = arr[ii];
    }
    r->a = 0;
    r->b = 24;
    for (i = 0; i < 165; i++)
        last = CCutil_lprand (r);
}


int CCutil_lprand (CCrandstate *r)
{
    int t;

    if (r->a-- == 0)
        r->a = 54;
    if (r->b-- == 0)
        r->b = 54;

    t = r->arr[r->a] - r->arr[r->b];

    if (t < 0)
        t += CC_PRANDMAX;

    r->arr[r->a] = t;

    return t;
}