// Copyright (C) 2001-2002 by Digital Mars
// All Rights Reserved
// www.digitalmars.com
// Written by Walter Bright

import std.c.string;
import std.c.stdlib;
import std.outofmemory;
import std.intrinsic;

//version = Asm86;
version = bitops;

struct GCBits
{
    const int BITS_PER_WORD = 32;
    const int BITS_SHIFT = 5;
    const int BITS_MASK = 31;

    uint *data = null;
    uint nwords = 0;	// allocated words in data[] excluding sentinals
    uint nbits = 0;	// number of bits in data[] excluding sentinals

    void Dtor()
    {
	if (data)
	{
	    free(data);
	    data = null;
	}
    }

    invariant
    {
	if (data)
	{
	    assert(nwords * data[0].sizeof * 8 >= nbits);
	}
    }

    void alloc(uint nbits)
    {
	this.nbits = nbits;
	nwords = (nbits + (BITS_PER_WORD - 1)) >> BITS_SHIFT;
	data = cast(uint *)calloc(nwords + 2, uint.sizeof);
	if (!data)
	    _d_OutOfMemory();
    }

    uint test(uint i)
    in
    {
	assert(i < nbits);
    }
    body
    {
	//return (cast(bit *)(data + 1))[i];
	return data[1 + (i >> BITS_SHIFT)] & (1 << (i & BITS_MASK));
    }

    void set(uint i)
    in
    {
	assert(i < nbits);
    }
    body
    {
	//(cast(bit *)(data + 1))[i] = 1;
	data[1 + (i >> BITS_SHIFT)] |= (1 << (i & BITS_MASK));
    }

    void clear(uint i)
    in
    {
	assert(i < nbits);
    }
    body
    {
	//(cast(bit *)(data + 1))[i] = 0;
	data[1 + (i >> BITS_SHIFT)] &= ~(1 << (i & BITS_MASK));
    }

    uint testClear(uint i)
    {
	version (bitops)
	{
	    return std.intrinsic.btr(data + 1, i);
	}
	else version (Asm86)
	{
	    asm
	    {
		naked			;
		mov	EAX,data[EAX]	;
		mov	ECX,i-4[ESP]	;
		btr	4[EAX],ECX	;
		sbb	EAX,EAX		;
		ret	4		;
	    }
	}
	else
	{   uint result;

	    //result = (cast(bit *)(data + 1))[i];
	    //(cast(bit *)(data + 1))[i] = 0;

	    uint *p = &data[1 + (i >> BITS_SHIFT)];
	    uint mask = (1 << (i & BITS_MASK));
	    result = *p & mask;
	    *p &= ~mask;
	    return result;
	}
    }

    void zero()
    {
	memset(data + 1, 0, nwords * uint.sizeof);
    }

    void copy(GCBits *f)
    in
    {
	assert(nwords == f.nwords);
    }
    body
    {
	memcpy(data + 1, f.data + 1, nwords * uint.sizeof);
    }

    uint *base()
    in
    {
	assert(data);
    }
    body
    {
	return data + 1;
    }
}

unittest
{
    GCBits b;

    b.alloc(786);
    assert(b.test(123) == 0);
    assert(b.testClear(123) == 0);
    b.set(123);
    assert(b.test(123) != 0);
    assert(b.testClear(123) != 0);
    assert(b.test(123) == 0);

    b.set(785);
    b.set(0);
    assert(b.test(785) != 0);
    assert(b.test(0) != 0);
    b.zero();
    assert(b.test(785) == 0);
    assert(b.test(0) == 0);

    GCBits b2;
    b2.alloc(786);
    b2.set(38);
    b.copy(&b2);
    assert(b.test(38) != 0);
    b2.Dtor();

    b.Dtor();
}

/+
void main()
{
}
+/