为什么不能在内核中使用科学记数法

Question

我正在尝试编写内核 (4.8.1) 模块，如果我使用

if (hrtimer_cancel(&hr_timer) == 1) {
         u64 remaining = ktime_to_ns(hrtimer_get_remaining(&hr_timer));
         printk("(%llu ns; %llu us)\n", remaining,
         (unsigned long long) (remaining/1e3));
}

它引发了这个错误

error: SSE register return with SSE disabled
   printk("\t\t(%llu ns; %llu us)\n",
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          remaining,
          ~~~~~~~~~~
          (unsigned long long) (remaining/1e3));
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

而如果我使用

if (hrtimer_cancel(&hr_timer) == 1) {
         u64 remaining = ktime_to_ns(hrtimer_get_remaining(&hr_timer));
         printk("(%llu ns; %llu us)\n", remaining,
         (unsigned long long) (remaining/1000));
}

它没有问题。

那么为什么不能在内核中使用科学计数法呢？我的意思是，我认为使用 1e3; 1e6; 1e9 而不是 1000; 1000000; 1000000000.

更容易和更易读

只是portability/robustness的问题吗？
或者类似的东西（在这种情况下）

You need ns? Use ktime_to_ns
You need us? Use ktime_to_us
You need ms? Use ktime_to_ms

P.S。我尝试了一个简单的 .c 程序，它没有问题

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

void error_handler(const char *msg)
{
    perror(msg);
    exit(EXIT_FAILURE);
}

unsigned long parse_num(const char *number)
{
    unsigned long v;
    char *p;
    errno = 0;

    v = strtoul(number, &p, 10);

    if (errno != 0 || *p != '[=13=]')
        error_handler("parse_num | strtoul");

    return v;
}

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        fprintf(stderr, "Usage: %s number_greater_than_1000\n", argv[0]);
        return EXIT_FAILURE;
    }

    unsigned long number = parse_num(argv[1]);

    if (number < 1e3 || number > 1e6)
    {
        fprintf(stderr, "Need to be a number in range (%lu, %lu)\n", (unsigned long) 1e3, (unsigned long) 1e6);
        return EXIT_FAILURE;
    }

    printf("Original: %lu\tScaled: %lu\n", number, (unsigned long) (number/1e3));

    return EXIT_SUCCESS;
}

Answer 1

1e3 不等同于 1000.

1000 是 int 类型的整型常量。 1e3 是一个 double 类型的浮点常量，等价于 1000.0。这使得 remaining/1e3 成为浮点除法，这正是编译器所抱怨的。

另见 SSE register return with SSE disabled。

为什么不能在内核中使用科学记数法

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