传递任意大小的整数来自前导到C [英] Passing arbitrary-sized integers from Prolog to C

问题描述

现在，我正在学习如何连接SICStus的Prolog用C code。

Right now, I'm learning how to interface SICStus Prolog with C code.

我想有/使用/看C实现任意大小的整数的汉明权的序言SICStus版本4。

I would like to have/use/see a C implementation of "Hamming weight" of arbitrary-sized integers in SICStus Prolog version 4.

在我看来，我需要进行测试条款类型的C函数（SP_is_integer）和C函数访问Prolog的条款（SP_get_integer，SP_get_integer_bytes）。

It seems to me that I need C functions for testing term types (SP_is_integer) and C functions for accessing Prolog terms (SP_get_integer, SP_get_integer_bytes).

不过，我不知道如何在便携，坚固的方式使用SP_get_integer_bytes。可否请你指出我的一些精心设计的固体C $ C $ç正是这样做？

However, I'm not sure how to use SP_get_integer_bytes in a portable, robust fashion. Could you please point me to some well-crafted solid C code doing just that?

推荐答案

使用它是这样的：

SP_term_ref tr = ... some term ...
int native = 0; // want portable, little endian
size_t buf_size = 0;

if (!SP_get_integer_bytes(tr, NULL, &buf_size, native)
    // if buf_size was updated, then there was not really an error
    && buf_size == 0)
{
    // Something wrong (e.g., not an integer)
    return ERROR;
}

// here buf_size > 0
void *buffer = SP_malloc(buf_size);

if (buffer == NULL)
{
    return ERROR;
}

if (!SP_get_integer_bytes(tr, buffer, &buf_size, native))
{
    // Something wrong. This would be surprising here
    error();
}

// Here buffer contains buf_size bytes, in
// twos-complement, with the least significant bytes at lowest index.
// ... do something with buffer ...

// finally clean up
SP_free(buffer);

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