49 lines
1.2 KiB
C
49 lines
1.2 KiB
C
#include <libowfat/fmt.h>
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static size_t asn1derlengthbytesneeded(unsigned long long l) {
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size_t needed;
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for (needed=1; (l>>=8)>0; ++needed) ;
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return needed;
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}
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/* write int in least amount of bytes, return number of bytes */
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/* as used in ASN.1 length */
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size_t fmt_asn1derlength(char* dest,unsigned long long l) {
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/* encoding is either l%128 or (0x80+number of bytes,bytes) */
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size_t i;
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if (l<128) {
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if (dest) *dest=l&0x7f;
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return 1;
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}
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for (i=1; i<sizeof l; ++i)
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if (!(l>>(i*8)))
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break;
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if (dest) {
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size_t j=i;
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*dest=(char)(0x80+i); ++dest;
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while (j) {
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--j;
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*dest=(char)((l>>(j*8))&0xff);
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++dest;
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}
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}
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return i+1;
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}
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#ifdef UNITTEST
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#include <assert.h>
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#include <string.h>
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int main() {
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char buf[100];
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#define zap() memset(buf,'_',sizeof buf)
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assert(fmt_asn1derlength(NULL,0)==1);
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zap(); assert(fmt_asn1derlength(buf,0)==1 && !memcmp(buf,"\x00_",2));
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assert(fmt_asn1derlength(NULL,0xc2)==2);
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zap(); assert(fmt_asn1derlength(buf,0xc2)==2 && !memcmp(buf,"\x81\xc2_",3));
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assert(fmt_asn1derlength(NULL,0x1234)==3);
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zap(); assert(fmt_asn1derlength(buf,0x1234)==3 && !memcmp(buf,"\x82\x12\x34_",3));
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return 0;
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}
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#endif
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