static unsigned int BN_STACK_pop(BN_STACK *st)
{
    return st->indexes[--(st->depth)];
}
['int ec_GFp_simple_dbl(const EC_GROUP *group, EC_POINT *r, const EC_POINT *a,\n                      BN_CTX *ctx)\n{\n    int (*field_mul) (const EC_GROUP *, BIGNUM *, const BIGNUM *,\n                      const BIGNUM *, BN_CTX *);\n    int (*field_sqr) (const EC_GROUP *, BIGNUM *, const BIGNUM *, BN_CTX *);\n    const BIGNUM *p;\n    BN_CTX *new_ctx = NULL;\n    BIGNUM *n0, *n1, *n2, *n3;\n    int ret = 0;\n    if (EC_POINT_is_at_infinity(group, a)) {\n        BN_zero(r->Z);\n        r->Z_is_one = 0;\n        return 1;\n    }\n    field_mul = group->meth->field_mul;\n    field_sqr = group->meth->field_sqr;\n    p = group->field;\n    if (ctx == NULL) {\n        ctx = new_ctx = BN_CTX_new();\n        if (ctx == NULL)\n            return 0;\n    }\n    BN_CTX_start(ctx);\n    n0 = BN_CTX_get(ctx);\n    n1 = BN_CTX_get(ctx);\n    n2 = BN_CTX_get(ctx);\n    n3 = BN_CTX_get(ctx);\n    if (n3 == NULL)\n        goto err;\n    if (a->Z_is_one) {\n        if (!field_sqr(group, n0, a->X, ctx))\n            goto err;\n        if (!BN_mod_lshift1_quick(n1, n0, p))\n            goto err;\n        if (!BN_mod_add_quick(n0, n0, n1, p))\n            goto err;\n        if (!BN_mod_add_quick(n1, n0, group->a, p))\n            goto err;\n    } else if (group->a_is_minus3) {\n        if (!field_sqr(group, n1, a->Z, ctx))\n            goto err;\n        if (!BN_mod_add_quick(n0, a->X, n1, p))\n            goto err;\n        if (!BN_mod_sub_quick(n2, a->X, n1, p))\n            goto err;\n        if (!field_mul(group, n1, n0, n2, ctx))\n            goto err;\n        if (!BN_mod_lshift1_quick(n0, n1, p))\n            goto err;\n        if (!BN_mod_add_quick(n1, n0, n1, p))\n            goto err;\n    } else {\n        if (!field_sqr(group, n0, a->X, ctx))\n            goto err;\n        if (!BN_mod_lshift1_quick(n1, n0, p))\n            goto err;\n        if (!BN_mod_add_quick(n0, n0, n1, p))\n            goto err;\n        if (!field_sqr(group, n1, a->Z, ctx))\n            goto err;\n        if (!field_sqr(group, n1, n1, ctx))\n            goto err;\n        if (!field_mul(group, n1, n1, group->a, ctx))\n            goto err;\n        if (!BN_mod_add_quick(n1, n1, n0, p))\n            goto err;\n    }\n    if (a->Z_is_one) {\n        if (!BN_copy(n0, a->Y))\n            goto err;\n    } else {\n        if (!field_mul(group, n0, a->Y, a->Z, ctx))\n            goto err;\n    }\n    if (!BN_mod_lshift1_quick(r->Z, n0, p))\n        goto err;\n    r->Z_is_one = 0;\n    if (!field_sqr(group, n3, a->Y, ctx))\n        goto err;\n    if (!field_mul(group, n2, a->X, n3, ctx))\n        goto err;\n    if (!BN_mod_lshift_quick(n2, n2, 2, p))\n        goto err;\n    if (!BN_mod_lshift1_quick(n0, n2, p))\n        goto err;\n    if (!field_sqr(group, r->X, n1, ctx))\n        goto err;\n    if (!BN_mod_sub_quick(r->X, r->X, n0, p))\n        goto err;\n    if (!field_sqr(group, n0, n3, ctx))\n        goto err;\n    if (!BN_mod_lshift_quick(n3, n0, 3, p))\n        goto err;\n    if (!BN_mod_sub_quick(n0, n2, r->X, p))\n        goto err;\n    if (!field_mul(group, n0, n1, n0, ctx))\n        goto err;\n    if (!BN_mod_sub_quick(r->Y, n0, n3, p))\n        goto err;\n    ret = 1;\n err:\n    BN_CTX_end(ctx);\n    BN_CTX_free(new_ctx);\n    return ret;\n}', 'void BN_CTX_start(BN_CTX *ctx)\n{\n    CTXDBG("ENTER BN_CTX_start()", ctx);\n    if (ctx->err_stack || ctx->too_many)\n        ctx->err_stack++;\n    else if (!BN_STACK_push(&ctx->stack, ctx->used)) {\n        BNerr(BN_F_BN_CTX_START, BN_R_TOO_MANY_TEMPORARY_VARIABLES);\n        ctx->err_stack++;\n    }\n    CTXDBG("LEAVE BN_CTX_start()", ctx);\n}', 'void BN_CTX_end(BN_CTX *ctx)\n{\n    CTXDBG("ENTER BN_CTX_end()", ctx);\n    if (ctx->err_stack)\n        ctx->err_stack--;\n    else {\n        unsigned int fp = BN_STACK_pop(&ctx->stack);\n        if (fp < ctx->used)\n            BN_POOL_release(&ctx->pool, ctx->used - fp);\n        ctx->used = fp;\n        ctx->too_many = 0;\n    }\n    CTXDBG("LEAVE BN_CTX_end()", ctx);\n}', 'static unsigned int BN_STACK_pop(BN_STACK *st)\n{\n    return st->indexes[--(st->depth)];\n}']