94 lines
2.4 KiB
C
94 lines
2.4 KiB
C
#include <assert.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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/*
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* Pack header data into a byte.
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* 3 bits are used for type (2^3 = 8 different types)
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* 5 bits are used for length (2^5 = 32 max length, unit is up to you)
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*/
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typedef enum {
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Ok = 0,
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OversizedType,
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OversizedLen,
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} Result;
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#define TYPE_LEN (4)
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#define LEN (4)
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Result msg_create_header(uint8_t type, uint8_t len, uint8_t *out);
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void msg_parse_header(uint8_t header, uint8_t *type_out, uint8_t *len_out);
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int main(void) {
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assert(TYPE_LEN + LEN <= 8);
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uint8_t maxlen = (1 << LEN) - 1;
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uint8_t maxtype = (1 << TYPE_LEN) - 1;
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{
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uint8_t hdr;
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Result res = msg_create_header(3, 8, &hdr);
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if (res == OversizedType)
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printf("The type is out of range");
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if (res == OversizedLen)
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printf("The length is out of range");
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printf("Header: 0x%02X\n", hdr);
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printf("Error: %d\n", res);
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uint8_t plen, ptype;
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msg_parse_header(hdr, &ptype, &plen);
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printf("Type: %d\n", ptype);
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printf("Len: %d\n", plen);
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}
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{
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printf("Max len: %d\n", maxlen);
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printf("Max type: %d\n", maxtype);
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uint8_t hdr;
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Result res = msg_create_header(maxtype, maxlen, &hdr);
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assert(res == Ok);
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uint8_t plen, ptype;
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msg_parse_header(hdr, &ptype, &plen);
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printf("plen: %d\n", plen);
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printf("ptype: %d\n", ptype);
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assert(ptype == maxtype);
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assert(plen == maxlen);
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}
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{
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for (int i = 0; i < 1000; i++) {
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uint8_t len = arc4random() % maxlen;
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uint8_t type = arc4random() % maxtype;
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uint8_t hdr;
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Result res = msg_create_header(type, len, &hdr);
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assert(res == Ok);
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uint8_t plen, ptype;
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msg_parse_header(hdr, &ptype, &plen);
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assert(ptype == type);
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assert(plen == len);
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}
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}
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return 0;
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}
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Result msg_create_header(uint8_t type, uint8_t len, uint8_t *out) {
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if (type > (1 << TYPE_LEN) - 1)
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return OversizedType;
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if (len > (1 << LEN) - 1)
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return OversizedLen;
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*out = (type << LEN) | (len & (0xFF >> TYPE_LEN));
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return Ok;
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}
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void msg_parse_header(uint8_t header, uint8_t *type_out, uint8_t *len_out) {
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*type_out = (header >> LEN) & ((1 << LEN) - 1);
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*len_out = header & (0xFF >> TYPE_LEN);
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}
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