text: /* crypto/bn/bn_ctx.c */
  /* Written by Ulf Moeller for the OpenSSL project. */
  /* ====================================================================
   * Copyright (c) 1998-2004 The OpenSSL Project.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer. 
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. All advertising materials mentioning features or use of this
   *    software must display the following acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
   *
   * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission. For written permission, please contact
   *    openssl-core@openssl.org.
   *
   * 5. Products derived from this software may not be called "OpenSSL"
   *    nor may "OpenSSL" appear in their names without prior written
   *    permission of the OpenSSL Project.
   *
   * 6. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
   *
   * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
   * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   * ====================================================================
   *
   * This product includes cryptographic software written by Eric Young
   * (eay@cryptsoft.com).  This product includes software written by Tim
   * Hudson (tjh@cryptsoft.com).
   *
   */
  
  #if !defined(BN_CTX_DEBUG) && !defined(BN_DEBUG)
  #ifndef NDEBUG
  #define NDEBUG
  #endif
  #endif
  
  #include <stdio.h>
  #include <assert.h>
  
  #include "cryptlib.h"
  #include "bn_lcl.h"
  
  /* TODO list
   *
   * 1. Check a bunch of "(words+1)" type hacks in various bignum functions and
   * check they can be safely removed.
   *  - Check +1 and other ugliness in BN_from_montgomery()
   *
   * 2. Consider allowing a BN_new_ex() that, at least, lets you specify an
   * appropriate 'block' size that will be honoured by bn_expand_internal() to
   * prevent piddly little reallocations. OTOH, profiling bignum expansions in
   * BN_CTX doesn't show this to be a big issue.
   */
  
  /* How many bignums are in each "pool item"; */
  #define BN_CTX_POOL_SIZE	16
  /* The stack frame info is resizing, set a first-time expansion size; */
  #define BN_CTX_START_FRAMES	32
  
  /***********/
  /* BN_POOL */
  /***********/
  
  /* A bundle of bignums that can be linked with other bundles */
  typedef struct bignum_pool_item
  	{
  	/* The bignum values */
  	BIGNUM vals[BN_CTX_POOL_SIZE];
  	/* Linked-list admin */
  	struct bignum_pool_item *prev, *next;
  	} BN_POOL_ITEM;
  /* A linked-list of bignums grouped in bundles */
  typedef struct bignum_pool
  	{
  	/* Linked-list admin */
  	BN_POOL_ITEM *head, *current, *tail;
  	/* Stack depth and allocation size */
  	unsigned used, size;
  	} BN_POOL;
  static void		BN_POOL_init(BN_POOL *);
  static void		BN_POOL_finish(BN_POOL *);
  #ifndef OPENSSL_NO_DEPRECATED
  static void		BN_POOL_reset(BN_POOL *);
  #endif
  static BIGNUM *		BN_POOL_get(BN_POOL *);
  static void		BN_POOL_release(BN_POOL *, unsigned int);
  
  /************/
  /* BN_STACK */
  /************/
  
  /* A wrapper to manage the "stack frames" */
  typedef struct bignum_ctx_stack
  	{
  	/* Array of indexes into the bignum stack */
  	unsigned int *indexes;
  	/* Number of stack frames, and the size of the allocated array */
  	unsigned int depth, size;
  	} BN_STACK;
  static void		BN_STACK_init(BN_STACK *);
  static void		BN_STACK_finish(BN_STACK *);
  #ifndef OPENSSL_NO_DEPRECATED
  static void		BN_STACK_reset(BN_STACK *);
  #endif
  static int		BN_STACK_push(BN_STACK *, unsigned int);
  static unsigned int	BN_STACK_pop(BN_STACK *);
  
  /**********/
  /* BN_CTX */
  /**********/
  
  /* The opaque BN_CTX type */
  struct bignum_ctx
  	{
  	/* The bignum bundles */
  	BN_POOL pool;
  	/* The "stack frames", if you will */
  	BN_STACK stack;
  	/* The number of bignums currently assigned */
  	unsigned int used;
  	/* Depth of stack overflow */
  	int err_stack;
  	/* Block "gets" until an "end" (compatibility behaviour) */
  	int too_many;
  	};
  
  /* Enable this to find BN_CTX bugs */
  #ifdef BN_CTX_DEBUG
  static const char *ctxdbg_cur = NULL;
  static void ctxdbg(BN_CTX *ctx)
  	{
  	unsigned int bnidx = 0, fpidx = 0;
  	BN_POOL_ITEM *item = ctx->pool.head;
  	BN_STACK *stack = &ctx->stack;
  	fprintf(stderr,"(%08x): ", (unsigned int)ctx);
  	while(bnidx < ctx->used)
  		{
  		fprintf(stderr,"%03x ", item->vals[bnidx++ % BN_CTX_POOL_SIZE].dmax);
  		if(!(bnidx % BN_CTX_POOL_SIZE))
  			item = item->next;
  		}
  	fprintf(stderr,"\n");
  	bnidx = 0;
  	fprintf(stderr,"          : ");
  	while(fpidx < stack->depth)
  		{
  		while(bnidx++ < stack->indexes[fpidx])
  			fprintf(stderr,"    ");
  		fprintf(stderr,"^^^ ");
  		bnidx++;
  		fpidx++;
  		}
  	fprintf(stderr,"\n");
  	}
  #define CTXDBG_ENTRY(str, ctx)	do { \
  				ctxdbg_cur = (str); \
  				fprintf(stderr,"Starting %s\n", ctxdbg_cur); \
  				ctxdbg(ctx); \
  				} while(0)
  #define CTXDBG_EXIT(ctx)	do { \
  				fprintf(stderr,"Ending %s\n", ctxdbg_cur); \
  				ctxdbg(ctx); \
  				} while(0)
  #define CTXDBG_RET(ctx,ret)
  #else
  #define CTXDBG_ENTRY(str, ctx)
  #define CTXDBG_EXIT(ctx)
  #define CTXDBG_RET(ctx,ret)
  #endif
  
  /* This function is an evil legacy and should not be used. This implementation
   * is WYSIWYG, though I've done my best. */
  #ifndef OPENSSL_NO_DEPRECATED
  void BN_CTX_init(BN_CTX *ctx)
  	{
  	/* Assume the caller obtained the context via BN_CTX_new() and so is
  	 * trying to reset it for use. Nothing else makes sense, least of all
  	 * binary compatibility from a time when they could declare a static
  	 * variable. */
  	BN_POOL_reset(&ctx->pool);
  	BN_STACK_reset(&ctx->stack);
  	ctx->used = 0;
  	ctx->err_stack = 0;
  	ctx->too_many = 0;
  	}
  #endif
  
  BN_CTX *BN_CTX_new(void)
  	{
  	BN_CTX *ret = OPENSSL_malloc(sizeof(BN_CTX));
  	if(!ret)
  		{
  		BNerr(BN_F_BN_CTX_NEW,ERR_R_MALLOC_FAILURE);
  		return NULL;
  		}
  	/* Initialise the structure */
  	BN_POOL_init(&ret->pool);
  	BN_STACK_init(&ret->stack);
  	ret->used = 0;
  	ret->err_stack = 0;
  	ret->too_many = 0;
  	return ret;
  	}
  
  void BN_CTX_free(BN_CTX *ctx)
  	{
  	if (ctx == NULL)
  		return;
  #ifdef BN_CTX_DEBUG
  	{
  	BN_POOL_ITEM *pool = ctx->pool.head;
  	fprintf(stderr,"BN_CTX_free, stack-size=%d, pool-bignums=%d\n",
  		ctx->stack.size, ctx->pool.size);
  	fprintf(stderr,"dmaxs: ");
  	while(pool) {
  		unsigned loop = 0;
  		while(loop < BN_CTX_POOL_SIZE)
  			fprintf(stderr,"%02x ", pool->vals[loop++].dmax);
  		pool = pool->next;
  	}
  	fprintf(stderr,"\n");
  	}
  #endif
  	BN_STACK_finish(&ctx->stack);
  	BN_POOL_finish(&ctx->pool);
  	OPENSSL_free(ctx);
  	}
  
  void BN_CTX_start(BN_CTX *ctx)
  	{
  	CTXDBG_ENTRY("BN_CTX_start", ctx);
  	/* If we're already overflowing ... */
  	if(ctx->err_stack || ctx->too_many)
  		ctx->err_stack++;
  	/* (Try to) get a new frame pointer */
  	else if(!BN_STACK_push(&ctx->stack, ctx->used))
  		{
  		BNerr(BN_F_BN_CTX_START,BN_R_TOO_MANY_TEMPORARY_VARIABLES);
  		ctx->err_stack++;
  		}
  	CTXDBG_EXIT(ctx);
  	}
  
  void BN_CTX_end(BN_CTX *ctx)
  	{
  	CTXDBG_ENTRY("BN_CTX_end", ctx);
  	if(ctx->err_stack)
  		ctx->err_stack--;
  	else
  		{
  		unsigned int fp = BN_STACK_pop(&ctx->stack);
  		/* Does this stack frame have anything to release? */
  		if(fp < ctx->used)
  			BN_POOL_release(&ctx->pool, ctx->used - fp);
  		ctx->used = fp;
  		/* Unjam "too_many" in case "get" had failed */
  		ctx->too_many = 0;
  		}
  	CTXDBG_EXIT(ctx);
  	}
  
  BIGNUM *BN_CTX_get(BN_CTX *ctx)
  	{
  	BIGNUM *ret;
  	CTXDBG_ENTRY("BN_CTX_get", ctx);
  	if(ctx->err_stack || ctx->too_many) return NULL;
  	if((ret = BN_POOL_get(&ctx->pool)) == NULL)
  		{
  		/* Setting too_many prevents repeated "get" attempts from
  		 * cluttering the error stack. */
  		ctx->too_many = 1;
  		BNerr(BN_F_BN_CTX_GET,BN_R_TOO_MANY_TEMPORARY_VARIABLES);
  		return NULL;
  		}
  	/* OK, make sure the returned bignum is "zero" */
  	BN_zero(ret);
  	ctx->used++;
  	CTXDBG_RET(ctx, ret);
  	return ret;
  	}
  
  /************/
  /* BN_STACK */
  /************/
  
  static void BN_STACK_init(BN_STACK *st)
  	{
  	st->indexes = NULL;
  	st->depth = st->size = 0;
  	}
  
  static void BN_STACK_finish(BN_STACK *st)
  	{
  	if(st->size) OPENSSL_free(st->indexes);
  	}
  
  #ifndef OPENSSL_NO_DEPRECATED
  static void BN_STACK_reset(BN_STACK *st)
  	{
  	st->depth = 0;
  	}
  #endif
  
  static int BN_STACK_push(BN_STACK *st, unsigned int idx)
  	{
  	if(st->depth == st->size)
  		/* Need to expand */
  		{
  		unsigned int newsize = (st->size ?
  				(st->size * 3 / 2) : BN_CTX_START_FRAMES);
  		unsigned int *newitems = OPENSSL_malloc(newsize *
  						sizeof(unsigned int));
  		if(!newitems) return 0;
  		if(st->depth)
  			memcpy(newitems, st->indexes, st->depth *
  						sizeof(unsigned int));
  		if(st->size) OPENSSL_free(st->indexes);
  		st->indexes = newitems;
  		st->size = newsize;
  		}
  	st->indexes[(st->depth)++] = idx;
  	return 1;
  	}
  
  static unsigned int BN_STACK_pop(BN_STACK *st)
  	{
  	return st->indexes[--(st->depth)];
  	}
  
  /***********/
  /* BN_POOL */
  /***********/
  
  static void BN_POOL_init(BN_POOL *p)
  	{
  	p->head = p->current = p->tail = NULL;
  	p->used = p->size = 0;
  	}
  
  static void BN_POOL_finish(BN_POOL *p)
  	{
  	while(p->head)
  		{
  		unsigned int loop = 0;
  		BIGNUM *bn = p->head->vals;
  		while(loop++ < BN_CTX_POOL_SIZE)
  			{
  			if(bn->d) BN_clear_free(bn);
  			bn++;
  			}
  		p->current = p->head->next;
  		OPENSSL_free(p->head);
  		p->head = p->current;
  		}
  	}
  
  #ifndef OPENSSL_NO_DEPRECATED
  static void BN_POOL_reset(BN_POOL *p)
  	{
  	BN_POOL_ITEM *item = p->head;
  	while(item)
  		{
  		unsigned int loop = 0;
  		BIGNUM *bn = item->vals;
  		while(loop++ < BN_CTX_POOL_SIZE)
  			{
  			if(bn->d) BN_clear(bn);
  			bn++;
  			}
  		item = item->next;
  		}
  	p->current = p->head;
  	p->used = 0;
  	}
  #endif
  
  static BIGNUM *BN_POOL_get(BN_POOL *p)
  	{
  	if(p->used == p->size)
  		{
  		BIGNUM *bn;
  		unsigned int loop = 0;
  		BN_POOL_ITEM *item = OPENSSL_malloc(sizeof(BN_POOL_ITEM));
  		if(!item) return NULL;
  		/* Initialise the structure */
  		bn = item->vals;
  		while(loop++ < BN_CTX_POOL_SIZE)
  			BN_init(bn++);
  		item->prev = p->tail;
  		item->next = NULL;
  		/* Link it in */
  		if(!p->head)
  			p->head = p->current = p->tail = item;
  		else
  			{
  			p->tail->next = item;
  			p->tail = item;
  			p->current = item;
  			}
  		p->size += BN_CTX_POOL_SIZE;
  		p->used++;
  		/* Return the first bignum from the new pool */
  		return item->vals;
  		}
  	if(!p->used)
  		p->current = p->head;
  	else if((p->used % BN_CTX_POOL_SIZE) == 0)
  		p->current = p->current->next;
  	return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);
  	}
  
  static void BN_POOL_release(BN_POOL *p, unsigned int num)
  	{
  	unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;
  	p->used -= num;
  	while(num--)
  		{
  		bn_check_top(p->current->vals + offset);
  		if(!offset)
  			{
  			offset = BN_CTX_POOL_SIZE - 1;
  			p->current = p->current->prev;
  			}
  		else
  			offset--;
  		}
  	}
  
  