Indices not pointers (#24)

* move cobs_decode_inplace to indices instead of pointers, do better error-checking and the code got smaller

* whitespace

* move cobs_encode_inplace to indice, smaller code + binary

* update docs

* fix C4706

* tighter windows warnings

* /WX not /Wx

* wow catch2 does not work with /WX

README.md

@@ -24,14 +24,14 @@ Also I didn't see as many unit tests as I'd have liked in the other libraries, e
 
 It's pretty small.
 ```
-❯ ../gcc-arm-none-eabi-10-2020-q4-major/bin/arm-none-eabi-gcc -mthumb -mcpu=cortex-m4 -Os -c cobs.c
-❯ ../gcc-arm-none-eabi-10-2020-q4-major/bin/arm-none-eabi-nm --print-size --size-sort cobs.o
-
-00000082 00000018 T cobs_encode_max      (24 bytes)
-0000004a 00000038 T cobs_decode_inplace  (56 bytes)
-00000000 0000004a T cobs_encode_inplace  (74 bytes)
-0000009a 0000007e T cobs_encode          (126 bytes)
-00000118 0000008e T cobs_decode          (142 bytes)
+❯ arm-none-eabi-gcc -mthumb -mcpu=cortex-m4 -Os -c cobs.c
+❯ arm-none-eabi-nm --print-size --size-sort cobs.o
+
+0000007a 00000018 T cobs_encode_max      (24 bytes)
+00000048 00000032 T cobs_decode_inplace  (50 bytes)
+00000000 00000048 T cobs_encode_inplace  (72 bytes)
+00000092 0000007a T cobs_encode          (122 bytes)
+0000010c 00000084 T cobs_decode          (132 bytes)
 ```
 
 ## Usage
@@ -93,7 +93,7 @@ cobs_ret_t const result = cobs_decode(encoded, encoded_len, decoded, sizeof(deco
 if (result == COBS_RET_SUCCESS) {
   // decoding succeeded, 'decoded' and 'decoded_len' hold details.
 } else {
-  // decoding failed, look to 'result' for details. 
+  // decoding failed, look to 'result' for details.
 }
 ```
 
@@ -117,7 +117,7 @@ if (result == COBS_RET_SUCCESS) {
 ```
 ## Developing
 
-`nanocobs` uses [catch2](https://github.com/catchorg/Catch2) for unit and functional testing; its unified mega-header is checked in to the `tests` directory. To build and run all tests on macOS or Linux, run `make -j` from a terminal. To build + run all tests on Windows, run the `vsvarsXX.bat` of your choice to set up the VS environment, then run `make-win.bat` (if you want to make that part better, pull requests are very welcome). 
+`nanocobs` uses [catch2](https://github.com/catchorg/Catch2) for unit and functional testing; its unified mega-header is checked in to the `tests` directory. To build and run all tests on macOS or Linux, run `make -j` from a terminal. To build + run all tests on Windows, run the `vsvarsXX.bat` of your choice to set up the VS environment, then run `make-win.bat` (if you want to make that part better, pull requests are very welcome).
 
 Also, it's really amazing how long it takes to compile the Catch2 amalgamated file, thanks C++!
 

cobs.c

@@ -4,60 +4,44 @@
 typedef unsigned char cobs_byte_t;
 
 cobs_ret_t cobs_encode_inplace(void *buf, unsigned len) {
-  if (!buf || (len < 2)) {
-    return COBS_RET_ERR_BAD_ARG;
-  }
+  if (!buf || (len < 2)) { return COBS_RET_ERR_BAD_ARG; }
 
-  cobs_byte_t *cur = (cobs_byte_t *)buf;
-  cobs_byte_t const *const end = cur + len - 1;
-  if ((*cur != COBS_ISV) || (*end != COBS_ISV)) {
+  cobs_byte_t *const src = (cobs_byte_t *)buf;
+  if ((src[0] != COBS_ISV) || (src[len - 1] != COBS_ISV)) {
     return COBS_RET_ERR_BAD_PAYLOAD;
   }
 
-  cobs_byte_t *patch = cur++;
-  while (cur < end) {
-    if (*cur == 0) {
-      unsigned const ofs = (unsigned)(cur - patch);
-      if (ofs > 255) {
-        return COBS_RET_ERR_BAD_PAYLOAD;
-      }
-      *patch = (cobs_byte_t)ofs;
+  unsigned patch = 0, cur = 1;
+  while (cur < len - 1) {
+    if (!src[cur]) {
+      unsigned const ofs = cur - patch;
+      if (ofs > 255) { return COBS_RET_ERR_BAD_PAYLOAD; }
+      src[patch] = (cobs_byte_t)ofs;
       patch = cur;
     }
     ++cur;
   }
-
-  unsigned const ofs = (unsigned)(cur - patch);
-  if (ofs > 255) {
-    return COBS_RET_ERR_BAD_PAYLOAD;
-  }
-  *patch = (cobs_byte_t)ofs;
-  *cur = 0;
+  unsigned const ofs = cur - patch;
+  if (ofs > 255) { return COBS_RET_ERR_BAD_PAYLOAD; }
+  src[patch] = (cobs_byte_t)ofs;
+  src[cur] = 0;
   return COBS_RET_SUCCESS;
 }
 
-cobs_ret_t cobs_decode_inplace(void *buf, unsigned len) {
-  if (!buf || (len < 2)) {
-    return COBS_RET_ERR_BAD_ARG;
-  }
+cobs_ret_t cobs_decode_inplace(void *buf, unsigned const len) {
+  if (!buf || (len < 2)) { return COBS_RET_ERR_BAD_ARG; }
 
-  cobs_byte_t *cur = (cobs_byte_t *)buf;
-  cobs_byte_t const *const end = cur + len - 1;
-  if ((*cur == 0) || (*end != 0)) {
-    return COBS_RET_ERR_BAD_PAYLOAD;
-  }
-
-  while (*cur) {
-    unsigned const ofs = *cur;
-    *cur = 0;
+  cobs_byte_t *const src = (cobs_byte_t *)buf;
+  unsigned ofs, cur = 0;
+  while ((ofs = src[cur]) != 0) {
+    src[cur] = 0;
     cur += ofs;
-    if (cur > end) {
-      return COBS_RET_ERR_BAD_PAYLOAD;
-    }
+    if (cur > len) { return COBS_RET_ERR_BAD_PAYLOAD; }
   }
 
-  *(cobs_byte_t *)buf = COBS_ISV;
-  *cur = COBS_ISV;
+  if (cur != len - 1) { return COBS_RET_ERR_BAD_PAYLOAD; }
+  src[0] = COBS_ISV;
+  src[len - 1] = COBS_ISV;
   return COBS_RET_SUCCESS;
 }
 

make-win.bat

@@ -1,4 +1,4 @@
-cl.exe /W4 /EHsc ^
+cl.exe /W4 /WX /EHsc ^
     cobs.c ^
     tests/test_cobs_encode_max.cc ^
     tests/test_cobs_encode.cc ^

tests/test_cobs_decode_inplace.cc

@@ -36,6 +36,8 @@ TEST_CASE("Inplace decoding validation", "[cobs_decode_inplace]") {
     REQUIRE( cobs_decode_vec(buf) == COBS_RET_ERR_BAD_PAYLOAD );
     buf = byte_vec_t{0x03, 0x01, 0x00}; // first byte jumps past end
     REQUIRE( cobs_decode_vec(buf) == COBS_RET_ERR_BAD_PAYLOAD );
+    buf = byte_vec_t{0x01, 0x00, 0x00}; // land on an interior 0x00
+    REQUIRE( cobs_decode_vec(buf) == COBS_RET_ERR_BAD_PAYLOAD );
   }
 }