printf - C++ Reference

Hash Table for Embedded Systems?

Hi all,
I have a CSV file of about 1500 elements that maps a long integer (uint32_t) to a 128-char ASCII binary string. When I want to access one of these strings, I use a fairly simple lookup strategy that returns this bitstring in a char array, which I then convert to a series of hex values for storage in a struct.
This is incredibly inefficient, and does too much disk access. Ideally, I'd want to have a hash table implementation with all normal functions, plus an option to reload from a predefined location on disk, with the added constraint that it be optimized for an embedded system (64kiB RAM allotted, 1GHz CPU; though this is a really low priority task e.g. Maximum NICE level).
Here's a partial C implementation of the current lookup method that compiles under -Werror, -Wall, -Wpedantic:
// reading a text file #include  #include  #include  #include  #include  #include  #define MAX_LINE_LENGTH 100 #define NUM_BITS_PER_CMD 96 //give 2 pointers and mode as input void print_bitstring(char *p) { for (int i = 0; i < strlen(p); i++) { if(i % 4 == 0 && i) printf(" "); if(i % 8 == 0 && i) printf("\n"); printf("%c", p[i]); } } void expander(uint32_t mode, char *f_b, char *s_b) { memset((unsigned char *)f_b, 0, strlen(f_b)); memset((unsigned char *)s_b, 0, strlen(f_b)); char temp1[MAX_LINE_LENGTH], temp2[2*MAX_LINE_LENGTH]; // Converting incoming mode to a string // reference: // u32_t format specifier found here: const int n = snprintf(NULL, 0, "%"PRIu32"", mode); assert(n > 0); char input[n+1]; int c = snprintf(input, n+1, "%"PRIu32"", mode); assert(input[n] == '\0'); assert(c == n); char command[MAX_LINE_LENGTH], mode_id[MAX_LINE_LENGTH], *pt, *line = NULL; FILE *fp; size_t len = 0; ssize_t read; fp = fopen("./lookupTable.csv", "r"); if (fp != NULL) { // Reading in lookup table line by line // reference: while ( (read = getline (&line, &len, fp)) != -1 ) { line[read - 1] = '\0'; char delimiter[] = ","; //size_t pos = 0; //mode_id = ""; // Read tokens from CSV file // reference: pt = strtok(line, delimiter); if (pt != NULL) { // Filling mode_id // reference: // I considered strlcpy, but strdup should work fine for our purposes. // mode_id = strdup(pt); strncpy(mode_id, pt, sizeof(mode_id)); #if(DEBUG) //printf("mode_id is %d bytes long.\n", strlen(mode_id)); #endif assert(mode_id != NULL); // strlcpy(mode_id, pt, MAX_LINE_LENGTH); pt = strtok(NULL, delimiter); } else { #if(DEBUG) printf("No comma found when parsing CSV! Exiting...\n"); #endif exit(EXIT_FAILURE); } if (pt != NULL) { strncpy(command, pt, sizeof(command)); //command = strdup(pt); assert(command != NULL); } else { #if(DEBUG) printf("No comma found when parsing CSV! Exiting...\n"); #endif exit(EXIT_FAILURE); } if(strcmp(input, mode_id) == 0) { #if(DEBUG) printf("Found a matching mode_id!\n"); #endif if(strlen(command) == NUM_BITS_PER_CMD) { strncpy(temp1, command, NUM_BITS_PER_CMD + 1); #if(DEBUG) printf("Copying command into f_b and s_b...\n"); #endif for(int i = 0; i < strlen(temp1); i++) { f_b[i]=temp1[i]; s_b[i]=temp1[i]; } } else { printf("Command was longer than %d bits. Detected length: %zu\n", NUM_BITS_PER_CMD, strlen(command)); printf("Command string:\n"); print_bitstring(command); strncpy(temp2, command, NUM_BITS_PER_CMD + 1); int j = 0; for(int i = 0; i < strlen(temp2); i++) { #if(DEBUG) if(i == 0) printf("Copying first %d bits into f_b\n", NUM_BITS_PER_CMD); if(i == NUM_BITS_PER_CMD) printf("Copying remaining %zu bits into s_b\n", strlen(temp2)-NUM_BITS_PER_CMD); #endif if(i < NUM_BITS_PER_CMD) { // Straightforward copy, maybe could just use strncpy? f_b[i]=temp2[i]; } else { // Overflows excess command bits into s_b s_b[j]=temp2[i]; j++; } } #if(DEBUG) if(j > 0) printf("Buffer contained %d extra bytes, copied into s_b\n", j); #endif } } } fclose(fp); } else { #if(DEBUG) printf("Unable to open file\n"); #endif exit(EXIT_FAILURE); } } int main (void) { uint32_t mode=1118074860;//32 bit mode ID // Corresponding shell command: grep 1118 lookupTable.csv | sed 's/.*,//' | sed -e "s/.\{8\}/&\n/g" char f_b[NUM_BITS_PER_CMD + 1], s_b[NUM_BITS_PER_CMD + 1]; //constant buffers to LIIB f_b[NUM_BITS_PER_CMD] = '\0'; s_b[NUM_BITS_PER_CMD] = '\0'; expander(mode, f_b, s_b); printf("Looping over first word (length: %zu)...\n", strlen(f_b)); print_bitstring(f_b); printf("\n"); printf("Looping over second word (length: %zu)...\n", strlen(s_b)); print_bitstring(s_b); return 0; } 
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C Program To Convert Decimal To Binary Number using ...

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