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))
		{
		/* I know this isn't BN_CTX_get, but ... */
		BNerr(BN_F_BN_CTX_GET,BN_R_TOO_MANY_TEMPORARY_VARIABLES);
		ctx->err_stack++;
		}
	CTXDBG_EXIT(ctx);
	}