int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl)
{
    EVP_MD_CTX_clear_flags(ctx, EVP_MD_CTX_FLAG_CLEANED);
#ifndef OPENSSL_NO_ENGINE
    /*
     * Whether it's nice or not, "Inits" can be used on "Final"'d contexts so
     * this context may already have an ENGINE! Try to avoid releasing the
     * previous handle, re-querying for an ENGINE, and having a
     * reinitialisation, when it may all be unnecessary.
     */
    if (ctx->engine && ctx->digest && (!type ||
                                       (type
                                        && (type->type ==
                                            ctx->digest->type))))
        goto skip_to_init;
    if (type) {
        /*
         * Ensure an ENGINE left lying around from last time is cleared (the
         * previous check attempted to avoid this if the same ENGINE and
         * EVP_MD could be used).
         */
        ENGINE_finish(ctx->engine);
        if (impl != NULL) {
            if (!ENGINE_init(impl)) {
                EVPerr(EVP_F_EVP_DIGESTINIT_EX, EVP_R_INITIALIZATION_ERROR);
                return 0;
            }
        } else {
            /* Ask if an ENGINE is reserved for this job */
            impl = ENGINE_get_digest_engine(type->type);
        }
        if (impl != NULL) {
            /* There's an ENGINE for this job ... (apparently) */
            const EVP_MD *d = ENGINE_get_digest(impl, type->type);

            if (d == NULL) {
                EVPerr(EVP_F_EVP_DIGESTINIT_EX, EVP_R_INITIALIZATION_ERROR);
                ENGINE_finish(impl);
                return 0;
            }
            /* We'll use the ENGINE's private digest definition */
            type = d;
            /*
             * Store the ENGINE functional reference so we know 'type' came
             * from an ENGINE and we need to release it when done.
             */
            ctx->engine = impl;
        } else
            ctx->engine = NULL;
    } else {
        if (!ctx->digest) {
            EVPerr(EVP_F_EVP_DIGESTINIT_EX, EVP_R_NO_DIGEST_SET);
            return 0;
        }
        type = ctx->digest;
    }
#endif
    if (ctx->digest != type) {
        if (ctx->digest && ctx->digest->ctx_size)
            OPENSSL_free(ctx->md_data);
        ctx->digest = type;
        if (!(ctx->flags & EVP_MD_CTX_FLAG_NO_INIT) && type->ctx_size) {
            ctx->update = type->update;
            ctx->md_data = OPENSSL_zalloc(type->ctx_size);
            if (ctx->md_data == NULL) {
                EVPerr(EVP_F_EVP_DIGESTINIT_EX, ERR_R_MALLOC_FAILURE);
                return 0;
            }
        }
    }
#ifndef OPENSSL_NO_ENGINE
 skip_to_init:
#endif
    if (ctx->pctx) {
        int r;
        r = EVP_PKEY_CTX_ctrl(ctx->pctx, -1, EVP_PKEY_OP_TYPE_SIG,
                              EVP_PKEY_CTRL_DIGESTINIT, 0, ctx);
        if (r <= 0 && (r != -2))
            return 0;
    }
    if (ctx->flags & EVP_MD_CTX_FLAG_NO_INIT)
        return 1;
    return ctx->digest->init(ctx);
}