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