Peter M. Groen / libmodbus

- allocate exact memory required to store node and service strings
  instead of around 1kb of static memory.
- accept NULL value of service to use default Modbus port number (502)
- unit test updated

The new documentation will be updated in another commit.

Even the newest visual studio use /VERSION:major[.minor]  .  
It means link.exe  /VERSION:1.0  just  need two version number .
If Version = 1.0.0 , when visual studio  link the program , vs will produce link error:

```
1>"/OUT:C:\Users\Lenovo\Desktop\libmodbus-master\src\win32\modbus.dll" "/VERSION:1.0.0" /INCREMENTAL:NO /NOLOGO ws2_32.lib kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /MANIFEST "/MANIFESTUAC:level='asInvoker' uiAccess='false'" /manifest:embed /DEBUG "/PDB:C:\Users\Lenovo\Desktop\libmodbus-master\src\win32\modbus.pdb" /MAP /SUBSYSTEM:CONSOLE /TLBID:1 "/IMPLIB:C:\Users\Lenovo\Desktop\libmodbus-master\src\win32\modbus.lib" /MACHINE:X86 /SAFESEH /DLL "C:\Users\Lenovo\Desktop\libmodbus-master\src\win32\/modbus.res"
1>"Debug\modbus-data.obj"
1>"Debug\modbus-rtu.obj"
1>"Debug\modbus-tcp.obj"
1>Debug\modbus.obj
1>LINK : fatal error LNK1117: option“VERSION:1.0.0” grammatical error
```
see: 
https://docs.microsoft.com/en-us/cpp/build/reference/version-version-information?view=msvc-160

Address check in single register / coil responses added

According to Modbus standard the address of single register / coils request and response must match

Co-authored-by: Heinrich Gsponer <heinrich.gsponer@siemens.com>

It converts float values depending on what order they come in.

This patch was modified from rm5248 [1]

[1] https://github.com/synexxus/libmodbus/commit/a511768e7fe7ec52d7bae1d9ae04e33f87a59627

This native libmodbus error code is defined but not used.

While handling MODBUS_FC_WRITE_AND_READ_REGISTERS, both address offsets
must be checked, i.e. the read and the write address must be within the
mapping range.

At the moment, only the read address was considered, it looks like a
simple copy and paste error, so let's fix it.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

Thank you @qqq89513

Thanks to @peternewman

When compiling with gcc and option -Wconversion it fixes the
warning message

  warning: conversion from ‘X’ {aka ‘x’} to ‘Y’ {aka ‘y’} may change value

Signed-off-by: José Bollo <jose.bollo@iot.bzh>

In case resulting value should be negative it is incorrect to use '+' operator to construct it from pieces, because highest bytes will result in negative number after bitwise shift while others will stay positive. Replacing addition with '|' should solve the issue.

Since SPDX release 3.0 LGPL-2.1+ became LGPL-2.1-or-later. Hence
replace the deprecated identifiers.

I can't believe I committed that copy/paste mistake.
Sorry Maor Vermucht and Or Peles, excepted naming your original
patch was OK.

Thank you Karl Palsson for your review.

Closes #461

This patch was contributed by Maor Vermucht and Or Peles from
VDOO Connected Trust.

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>

Thanks to @JCWren

I hope this was the correct place to fix it. I don't know asciidoc.

Found with the help of clang-format (from another branch)

According to the Modbus standard, the unit identifier is choosen by the
TCP client and can be any value:

"This field is used for intra-system routing purpose.  It is typically
used to communicate to a MODBUS+ or a MODBUS serial line slave through a
gateway between an Ethernet TCP-IP network and a MODBUS serial line.
This field is set by the MODBUS Client in the request and must be returned
with the same value in the response by the server."

So the current check in modbus_reply must be extended to check whether
we are in a RTU or TCP context.

Also the unit-test has to be adjusted.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

fixed small typo

This reverts commit 1d3c6401f8186b54453ba64606758a90b6ec3fca.

TravisCI reports:
../src/.libs/libmodbus.so: undefined reference to `__builtin_bswap16'

with gcc 4.6.3

Thanks to dreamflow for the issue.

Current code could dereference NULL pointer in case an inner
malloc fails. Check for this and exit gracefully.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

EMBBADCRC, not EMBADCRC