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Re: [Chicken-users] call Chicken Scheme from C and pass a bytevector

From: Felix
Subject: Re: [Chicken-users] call Chicken Scheme from C and pass a bytevector
Date: Fri, 28 Jun 2013 13:48:44 +0200 (CEST)

> Hum ... this has potential.
>   struct ipv4_addr_struct {
>     C_header tag;
>     uint8_t *octets;
>   };
>   typedef struct ipv4_addr_struct ipv4_addr;
>   static const C_header BTREE_TAG =
>     ((sizeof(ipv4_addr) - sizeof(C_header)) /
>     sizeof(C_word)) | C_BYTEVECTOR_TYPE;

Actually, a SRFI-4 numeric vector holds a tag (C_STRUCTURE_TYPE | 2),
a pointer to a Scheme symbol and a pointer to another Scheme "block",
which again holds a tag (C_BYTEVECTOR_TYPE | bytecount) with the
binary data directly following.

> This would be handled by the GC, right?

No, pointers pointing outside of the Scheme heap are simply
ignored by the GC.

> Would Scheme be able to convert or use this as a u8vector or would it
> be a blob which I could convert with blob->u8vector/shared ?

If you build a structure like I said above, it will be a SRFI-4 XXXvector,
but it might be easier to build only the "blob" (or bytevector). And
use "blob->..." to convert it. "blob->XXXvector" will also copy it into
the garbage collected heap.


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