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day 6, task 2 solved

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Felix Suchert 2022-12-28 12:03:48 +01:00
parent 8cb3eb85f5
commit d269b05042
Signed by: feliix42
GPG key ID: 24363525EA0E8A99
1 changed files with 61 additions and 13 deletions
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74
day_6/parser.y
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@ -8,14 +8,21 @@
%code requires { %code requires {
#include <stdbool.h> #include <stdbool.h>
#define BUFSIZE 14
typedef void* yyscan_t; typedef void* yyscan_t;
struct parser_state { struct parser_state {
// for storing the most recently read 4 chars // for storing the most recently read 14 chars
char buffer[4]; char buffer[BUFSIZE];
// location tracker // location tracker
unsigned long loc; unsigned long loc;
bool found_start;
bool found_start_of_packet;
unsigned long packet_start;
bool found_start_of_msg;
unsigned long msg_start;
bool check_matrix[26]; bool check_matrix[26];
}; };
@ -76,32 +83,69 @@ msg
bit bit
: CHAR { : CHAR {
if (!state->found_start) { if (!state->found_start_of_packet || !state->found_start_of_msg) {
state->loc++; state->loc++;
// left shift existing data // left shift existing data
for (int i = 0; i < 3; i++) { for (int i = 0; i < (BUFSIZE-1); i++) {
state->buffer[i] = state->buffer[i+1]; state->buffer[i] = state->buffer[i+1];
} }
state->buffer[3] = $1; state->buffer[BUFSIZE-1] = $1;
// check whether condition is met // check whether condition is met
// offset array indices by the base -- 'a' // offset array indices by the base -- 'a'
char offset = 'a'; char offset = 'a';
state->found_start = true; // Search for start of packet
for (int i = 0; i < 4; i++) { bool search_sop = !state->found_start_of_packet; // sop - start of packet
bool search_som = !state->found_start_of_msg; // som - start of message
if (search_sop) {
state->found_start_of_packet = true;
}
if (search_som) {
state->found_start_of_msg = true;
}
// the start of packet only concerns itself with the last 4 characters read; the start of message with the last 14
// hence, we check the last 4 first, then the rest
for (int i = BUFSIZE - 4; i < BUFSIZE; i++) {
if (!state->check_matrix[state->buffer[i] - offset]) { if (!state->check_matrix[state->buffer[i] - offset]) {
state->check_matrix[state->buffer[i] - offset] = true; state->check_matrix[state->buffer[i] - offset] = true;
} else { } else {
state->found_start = false; if (search_sop) {
state->found_start_of_packet = false;
}
if (search_som) {
state->found_start_of_msg = false;
}
break; break;
} }
} }
// now check the remaining elements
for (int i = 0; i < BUFSIZE - 4; i++) {
if (!state->check_matrix[state->buffer[i] - offset]) {
state->check_matrix[state->buffer[i] - offset] = true;
} else {
if (search_som) {
state->found_start_of_msg = false;
}
break;
}
}
if (search_sop && state->found_start_of_packet) {
state->packet_start = state->loc;
}
if (search_som && state->found_start_of_msg) {
state->msg_start = state->loc;
}
// housekeeping; reset the fields to false // housekeeping; reset the fields to false
for (int i = 0; i < 4; i++) { for (int i = 0; i < BUFSIZE; i++) {
state->check_matrix[state->buffer[i] - offset] = false; state->check_matrix[state->buffer[i] - offset] = false;
} }
} }
@ -113,11 +157,14 @@ bit
int main(void) { int main(void) {
struct parser_state parser_state; struct parser_state parser_state;
for (int i = 0; i < 4; i++) { for (int i = 0; i < BUFSIZE; i++) {
parser_state.buffer[i] = 'a'; parser_state.buffer[i] = 'a';
} }
parser_state.loc = 0; parser_state.loc = 0;
parser_state.found_start = false; parser_state.packet_start = 0;
parser_state.msg_start = 0;
parser_state.found_start_of_packet = false;
parser_state.found_start_of_msg = false;
yyscan_t scanner; yyscan_t scanner;
if (yylex_init(&scanner)) { if (yylex_init(&scanner)) {
@ -133,7 +180,8 @@ int main(void) {
yylex_destroy(scanner); yylex_destroy(scanner);
printf("First start-of-packet marker detected at: %lu\n", parser_state.loc); printf("First start-of-packet marker detected at: %lu\n", parser_state.packet_start);
printf("First start-of-message marker detected at: %lu\n", parser_state.msg_start);
return 0; return 0;
} }