Mirror of :pserver:cvs@cvs.fefe.de:/cvs libowfat https://www.fefe.de/libowfat/
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#include "fmt.h"
/* write int in least amount of bytes, return number of bytes */
/* as used in ASN.1 DER tag */
size_t fmt_asn1dertag(char* dest,unsigned long long l) {
/* high bit says if more bytes are coming, lower 7 bits are payload; big endian */
size_t n=0,i;
unsigned long long t;
for (t=l, n=1; t>0x7f; t>>=7) ++n;
for (i=0; i<n; ++i) {
if (dest) dest[n-i-1]=(char)(((i!=0)<<7) | (char)(l&0x7f));
return i;
#include <assert.h>
#include <string.h>
char buf[100];
void zap() { size_t i; for (i=0; i<sizeof(buf); ++i) buf[i]='_'; }
int main() {
zap(); assert(fmt_asn1dertag(buf,0)==1 && !memcmp(buf,"\x00_",2));
zap(); assert(fmt_asn1dertag(buf,0xc2)==2 && !memcmp(buf,"\x81\x42_",3));
return 0;