forked from vieter-v/libvieter
336 lines
7.9 KiB
C
336 lines
7.9 KiB
C
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#include "expression.h"
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// This prefix is needed to properly compile
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const uint8_t parse_month_days[] = {31, 28, 31, 30, 31, 30,
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31, 31, 30, 31, 30, 31};
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// Allowed value ranges for the minute, hour, day and month field
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const uint8_t min[4] = {0, 0, 1, 1};
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const uint8_t max[4] = {59, 23, 31, 12};
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const uint8_t min_parts = 2;
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const uint8_t max_parts = 4;
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// Convert a string into a uint8_t value by parsing it using atoi and checking
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// whether it's contained within the given range
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#define SAFE_ATOI(v, s, min, max) \
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int _##v = atoi(s); \
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if ((_##v) == 0 && strcmp((s), "0") != 0) { \
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return cron_parse_invalid_number; \
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} \
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if (((_##v) < (min)) || ((_##v) > (max))) { \
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return cron_parse_out_of_range; \
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} \
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v = (uint8_t)(_##v);
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#define MAX(x, y) (((x) > (y)) ? (x) : (y))
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/**
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* Given a range expression, produce a bit field defining what numbers in the
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* min-max range the expression represents. Bit 0 (starting from the
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* right) corresponds to min, the bit max - min to max. All trailing bits
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* after this should be ignored. The given bitfield is modified in-place, so
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* multiple calls of this function can be performed on the same value to create
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* the effect of ORing their values.
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*
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* A range expression has one of the following forms:
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*
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* - *
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* - a
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* - a-b
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* - a/c
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* - a-b/c
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*/
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cron_parse_error ce_parse_range(uint64_t *out, char *s, uint8_t min,
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uint8_t max) {
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size_t slash_index = 0, dash_index = 0;
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size_t s_index = 0;
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char cur_char;
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bool is_valid_character;
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while ((cur_char = s[s_index]) != '\0') {
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is_valid_character = cur_char == '/' || cur_char == '-' ||
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cur_char == '*' ||
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(cur_char >= '0' && cur_char <= '9');
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if (!is_valid_character) {
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return cron_parse_invalid_expression;
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}
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if (cur_char == '/') {
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if (s_index == 0 || slash_index != 0) {
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return cron_parse_invalid_expression;
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}
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slash_index = s_index;
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s[s_index] = '\0';
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} else if (cur_char == '-') {
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// At most one dash is allowed, and it must be before the slash
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if (s_index == 0 || dash_index != 0 || slash_index != 0) {
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return cron_parse_invalid_expression;
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}
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dash_index = s_index;
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s[s_index] = '\0';
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}
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s_index++;
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}
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uint8_t start;
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uint8_t end = max;
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uint8_t interval = 0;
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if (s[0] == '*') {
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if (s[1] != '\0' || dash_index != 0) {
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return cron_parse_invalid_expression;
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}
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start = min;
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interval = 1;
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} else {
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SAFE_ATOI(start, s, min, max);
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if (dash_index > 0) {
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SAFE_ATOI(end, &s[dash_index + 1], min, max);
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interval = 1;
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}
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}
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if (slash_index > 0) {
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SAFE_ATOI(interval, &s[slash_index + 1], 1, max - min);
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}
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if (interval == 0) {
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*out |= ((uint64_t)1) << (start - min);
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} else {
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while (start <= end) {
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*out |= ((uint64_t)1) << (start - min);
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start += interval;
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}
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}
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return cron_parse_ok;
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}
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/*
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* Given an expression part, produce a bitfield defining what numbers in the
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* min-max range the part represents. A part consists of one or more range
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* expressions, separated by commas.
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*/
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cron_parse_error ce_parse_part(uint64_t *out, char *s, uint8_t min,
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uint8_t max) {
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*out = 0;
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char *next;
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cron_parse_error res;
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while ((next = strchr(s, ',')) != NULL) {
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next[0] = '\0';
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res = ce_parse_range(out, s, min, max);
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if (res != cron_parse_ok) {
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return res;
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}
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s = next + 1;
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}
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// Make sure to parse the final range as well
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return ce_parse_range(out, s, min, max);
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}
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/*
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* Return how many bits are set in the bitfield, better known as popcount. I
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* added my own implementation (taken from my algorithms course) as I don't want
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* to be dependent on GCC-specific extensions.
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*/
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uint8_t uint64_t_popcount(uint64_t n) {
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uint8_t set_bits = 0;
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while (n != 0) {
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// This sets the least significant bit to zero (very cool)
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n &= n - 1;
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set_bits++;
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}
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return set_bits;
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}
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/*
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* Convert a bitfield into an array containing the numbers in the min-max range
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* it represents.
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*/
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uint8_t bf_to_nums(uint8_t **out, uint64_t bf, uint8_t min, uint8_t max) {
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// Each bit field only has `max - min + 1` meaningful bits. All other bits
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// should be ignored, and can be any value. By shifting the bit field back
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// and forth, we set these excessive bits to zero, ensuring popcount returns
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// the correct value.
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uint8_t excess_bits = 64 - (max - min + 1);
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bf = (bf << excess_bits) >> excess_bits;
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uint8_t size = uint64_t_popcount(bf);
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uint8_t *buf = malloc(size * sizeof(uint8_t));
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uint8_t bit_index = 0, buf_index = 0;
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while (buf_index < size && bit_index <= max - min) {
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if (((uint64_t)1 << bit_index) & bf) {
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// Resize buffer if needed
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buf[buf_index] = min + bit_index;
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buf_index++;
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}
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bit_index++;
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}
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*out = buf;
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return size;
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}
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/*
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* Parse a cron expression string into a cron_expression struct.
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*/
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cron_parse_error ce_parse_expression(cron_expression *out,
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const char *expression) {
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// The parsing functions modify the input string in-place
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char *s = strdup(expression);
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char *orig_s = s;
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cron_parse_error res = cron_parse_ok;
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// First we divide the input string into its parts, divided by spaces.
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// Each part is delimited by a NULL byte.
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uint8_t part_count = 0;
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char *parts[max_parts];
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char *next_space;
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// Skip leading spaces
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size_t offset = 0;
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while (s[offset] == ' ') {
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offset++;
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}
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s += offset;
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while (part_count < max_parts && ((next_space = strchr(s, ' ')) != NULL)) {
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next_space[0] = '\0';
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parts[part_count] = s;
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part_count++;
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// Skip multiple spaces
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offset = 1;
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while (next_space[offset] == ' ') {
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offset++;
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}
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s = next_space + offset;
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}
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// Each iteration of the loop skips all trailing spaces. This means that, if
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// s[0] isn't '\0', there's still another part before the end of the string.
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if (s[0] != '\0') {
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if (part_count == max_parts) {
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res = cron_parse_too_many_parts;
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goto end;
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}
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parts[part_count] = s;
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part_count++;
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}
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if (part_count < min_parts) {
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res = cron_parse_not_enough_parts;
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goto end;
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}
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// We now parse the parts in reverse. This is because the month part
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// determines the maximum value of the day part.
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uint64_t bit_field = 0;
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// Months
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if (part_count >= 4) {
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res = ce_parse_part(&bit_field, parts[3], min[3], max[3]);
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if (res != cron_parse_ok) {
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goto end;
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}
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out->month_count = bf_to_nums(&out->months, bit_field, min[3], max[3]);
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}
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// If months aren't provided, they're replaced with a *
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else {
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out->month_count = bf_to_nums(&out->months, ~0, min[3], max[3]);
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}
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// Determine what the largest allowed day value is, given the months
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uint8_t max_day_value = 0;
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for (uint8_t i = 0; i < out->month_count; i++) {
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max_day_value =
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MAX(max_day_value, parse_month_days[out->months[i] - 1]);
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}
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// Days
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if (part_count >= 3) {
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bit_field = 0;
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res = ce_parse_part(&bit_field, parts[2], min[2], max_day_value);
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if (res != cron_parse_ok) {
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free(out->months);
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goto end;
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}
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out->day_count =
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bf_to_nums(&out->days, bit_field, min[2], max_day_value);
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}
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// If days aren't provided, they're replaced with a *
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else {
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out->day_count = bf_to_nums(&out->days, ~0, min[2], max_day_value);
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}
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// Hours
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bit_field = 0;
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res = ce_parse_part(&bit_field, parts[1], min[1], max[1]);
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if (res != cron_parse_ok) {
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free(out->months);
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free(out->days);
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goto end;
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}
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out->hour_count = bf_to_nums(&out->hours, bit_field, min[1], max[1]);
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// Minutes
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bit_field = 0;
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res = ce_parse_part(&bit_field, parts[0], min[0], max[0]);
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if (res != cron_parse_ok) {
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free(out->months);
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free(out->days);
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free(out->hours);
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goto end;
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}
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out->minute_count = bf_to_nums(&out->minutes, bit_field, min[0], max[0]);
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end:
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// s is cloned
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free(orig_s);
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return res;
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}
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