bn_check_top(r);
int BN_mod_exp_recp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,		    const BIGNUM *m, BN_CTX *ctx)	{	int i,j,bits,ret=0,wstart,wend,window,wvalue;	int start=1,ts=0;	BIGNUM *aa;	BIGNUM val[TABLE_SIZE];	BN_RECP_CTX recp;	bits=BN_num_bits(p);	if (bits == 0)		{		ret = BN_one(r);		return ret;		}	BN_CTX_start(ctx);	if ((aa = BN_CTX_get(ctx)) == NULL) goto err;	BN_RECP_CTX_init(&recp);	if (m->neg)		{		/* ignore sign of 'm' */		if (!BN_copy(aa, m)) goto err;		aa->neg = 0;		if (BN_RECP_CTX_set(&recp,aa,ctx) <= 0) goto err;		}	else		{		if (BN_RECP_CTX_set(&recp,m,ctx) <= 0) goto err;		}	BN_init(&(val[0]));	ts=1;	if (!BN_nnmod(&(val[0]),a,m,ctx)) goto err;		/* 1 */	if (BN_is_zero(&(val[0])))		{		ret = BN_zero(r);		goto err;		}	window = BN_window_bits_for_exponent_size(bits);	if (window > 1)		{		if (!BN_mod_mul_reciprocal(aa,&(val[0]),&(val[0]),&recp,ctx))			goto err;				/* 2 */		j=1<<(window-1);		for (i=1; i<j; i++)			{			BN_init(&val[i]);			if (!BN_mod_mul_reciprocal(&(val[i]),&(val[i-1]),aa,&recp,ctx))				goto err;			}		ts=i;		}			start=1;	/* This is used to avoid multiplication etc			 * when there is only the value '1' in the			 * buffer. */	wvalue=0;	/* The 'value' of the window */	wstart=bits-1;	/* The top bit of the window */	wend=0;		/* The bottom bit of the window */	if (!BN_one(r)) goto err;	for (;;)		{		if (BN_is_bit_set(p,wstart) == 0)			{			if (!start)				if (!BN_mod_mul_reciprocal(r,r,r,&recp,ctx))				goto err;			if (wstart == 0) break;			wstart--;			continue;			}		/* We now have wstart on a 'set' bit, we now need to work out		 * how bit a window to do.  To do this we need to scan		 * forward until the last set bit before the end of the		 * window */		j=wstart;		wvalue=1;		wend=0;		for (i=1; i<window; i++)			{			if (wstart-i < 0) break;			if (BN_is_bit_set(p,wstart-i))				{				wvalue<<=(i-wend);				wvalue|=1;				wend=i;				}			}		/* wend is the size of the current window */		j=wend+1;		/* add the 'bytes above' */		if (!start)			for (i=0; i<j; i++)				{				if (!BN_mod_mul_reciprocal(r,r,r,&recp,ctx))					goto err;				}				/* wvalue will be an odd number < 2^window */		if (!BN_mod_mul_reciprocal(r,r,&(val[wvalue>>1]),&recp,ctx))			goto err;		/* move the 'window' down further */		wstart-=wend+1;		wvalue=0;		start=0;		if (wstart < 0) break;		}	ret=1;err:	BN_CTX_end(ctx);	for (i=0; i<ts; i++)		BN_clear_free(&(val[i]));	BN_RECP_CTX_free(&recp);	return(ret);	}