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How to convert NTP time to Unix Epoch time in C language (Linux)
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| #include <stdio.h> | |
| #include <stdlib.h> | |
| #include <time.h> | |
| #include <stdint.h> | |
| #include <getopt.h> | |
| #define OFFSET 2208988800ULL | |
| void ntp2tv(uint8_t ntp[8], struct timeval *tv) | |
| { | |
| uint64_t aux = 0; | |
| uint8_t *p = ntp; | |
| int i; | |
| /* we get the ntp in network byte order, so we must | |
| * convert it to host byte order. */ | |
| for (i = 0; i < sizeof ntp / 2; i++) { | |
| aux <<= 8; | |
| aux |= *p++; | |
| } /* for */ | |
| /* now we have in aux the NTP seconds offset */ | |
| aux -= OFFSET; | |
| tv->tv_sec = aux; | |
| /* let's go with the fraction of second */ | |
| aux = 0; | |
| for (; i < sizeof ntp; i++) { | |
| aux <<= 8; | |
| aux |= *p++; | |
| } /* for */ | |
| /* now we have in aux the NTP fraction (0..2^32-1) */ | |
| aux *= 1000000; /* multiply by 1e6 */ | |
| aux >>= 32; /* and divide by 2^32 */ | |
| tv->tv_usec = aux; | |
| } /* ntp2tv */ | |
| void tv2ntp(struct timeval *tv, uint8_t ntp[8]) | |
| { | |
| uint64_t aux = 0; | |
| uint8_t *p = ntp + sizeof ntp; | |
| int i; | |
| aux = tv->tv_usec; | |
| aux <<= 32; | |
| aux /= 1000000; | |
| /* we set the ntp in network byte order */ | |
| for (i = 0; i < sizeof ntp/2; i++) { | |
| *--p = aux & 0xff; | |
| aux >>= 8; | |
| } /* for */ | |
| aux = tv->tv_sec; | |
| aux += OFFSET; | |
| /* let's go with the fraction of second */ | |
| for (; i < sizeof ntp; i++) { | |
| *--p = aux & 0xff; | |
| aux >>= 8; | |
| } /* for */ | |
| } /* ntp2tv */ | |
| size_t print_tv(struct timeval *t) | |
| { | |
| return printf("%ld.%06ld\n", t->tv_sec, t->tv_usec); | |
| } | |
| size_t print_ntp(uint8_t ntp[8]) | |
| { | |
| int i; | |
| int res = 0; | |
| for (i = 0; i < sizeof ntp; i++) { | |
| if (i == sizeof ntp / 2) | |
| res += printf("."); | |
| res += printf("%02x", ntp[i]); | |
| } /* for */ | |
| res += printf("\n"); | |
| return res; | |
| } /* print_ntp */ | |
| int main(int argc, char *argv[]) | |
| { | |
| struct timeval t; | |
| uint8_t ntp[8]; | |
| gettimeofday(&t, NULL); | |
| printf("tv2ntp\n"); | |
| tv2ntp(&t, ntp); | |
| printf("tv : "); print_tv(&t); | |
| printf("ntp: "); print_ntp(ntp); | |
| printf("ntp2tv\n"); | |
| ntp2tv(ntp, &t); | |
| printf("tv : "); print_tv(&t); | |
| printf("ntp: "); print_ntp(ntp); | |
| } |
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