James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> + * Copyright (C) 2019 James.Bottomley@xxxxxxxxxxxxxxxxxxxxx
2020?
> +unsigned char *
> +asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
> + s64 integer);
I wonder if we should actually use u8 rather than unsigned char for data
pointers like this. That applies to asn1_ber_decoder() also.
You should be able to precalculate the length from fls64() or ilog2(), e.g.:
static size_t asn1_uint_len(unsigned long long integer)
{
size_t l = integer ? fls64(integer) : 1;
return l / 8 + 1;
}
See attached toy program.
> +/**
> + * asn1_encode_tag() - add a tag for optional or explicit value
> + * @data: pointer to place tag at
> + * @end_data: end of data pointer, points one beyond last usable byte in @data
> + * @tag: tag to be placed
> + * @string: the data to be tagged
> + * @len: the length of the data to be tagged
> + *
> + * Note this currently only handles short form tags < 31. To encode
> + * in place pass a NULL @string and -1 for @len; all this will do is
> + * add an indefinite length tag and update the data pointer to the
> + * place where the tag contents should be placed. After the data is
> + * placed, repeat the prior statement but now with the known length.
> + * In order to avoid having to keep both before and after pointers,
> + * the repeat expects to be called with @data pointing to where the
> + * first encode placed it.
> + */
I wonder if it's worth appending a note to the comment that if indefinite
length encoding is selected, then the result is not DER-compliant and may not
be CER-compliant since you're advertising BER/DER/CER.
> + if (*data_len < 1)
> + return -EINVAL;
ENOBUFS? I guess it doesn't really matter.
David
---
#include <stdio.h>
static inline int fls64(unsigned long long x)
{
int bitpos = -1;
/*
* AMD64 says BSRQ won't clobber the dest reg if x==0; Intel64 says the
* dest reg is undefined if x==0, but their CPU architect says its
* value is written to set it to the same as before.
*/
asm("bsrq %1,%q0"
: "+r" (bitpos)
: "rm" (x));
return bitpos + 1;
}
static const unsigned long long vals[] = {
0x1000000, 0xffffff, 0x800000, 0x7fffff,
0x100000, 0xfffff, 0x80000, 0x7ffff,
0x10000, 0xffff, 0x8000, 0x7fff,
0x1000, 0xfff, 0x800, 0x7ff,
0x100, 0xff, 0x80, 0x7f,
3, 2, 1, 0
};
static size_t asn1_uint_len(unsigned long long integer)
{
size_t l = integer ? fls64(integer) : 1;
return l / 8 + 1;
}
int main()
{
const unsigned long long *p = vals;
unsigned long long integer;
do {
integer = *p++;
printf("len: %16llx -> %zu\n", integer, asn1_uint_len(integer));
} while (integer);
}
