Remove dependency on internal headers

[mkoncek]

This commit completely removes the need to include internal headers and expands error macros. This greatly help us with packaging as now only the public headers are required.

[mkoncek]

@luben I see 3 options: 1) Call into libzstd ZSTD_getErrorCode

• no need to define our own macros
• the function call still does argument validity checking which may be unwanted 2) introduce our own header which implements the behaviour using a macro or a custom helper function 3) just use -ZSTD_error_*
• short and readable
• someone would need to go thru all its uses in code and verify that the explicit casts were not needed.

[mkoncek]

Unrelated, but I found this:

$ grep -n '[^-]ZSTD_error' *.c
jni_fast_zstd.c:336:        return ZSTD_error_srcSize_wrong;
jni_zstd.c:198:    if (ddict == NULL) return ZSTD_error_dictionary_wrong;
jni_zstd.c:232:    if (cdict == NULL) return ZSTD_error_dictionary_wrong;
jni_zstd.c:363:      return ZSTD_error_##err; \

The first three cases where you don't return the negative error code, is that correct? Everywhere else you do return negative values.

[mkoncek]

This is my suggestion https://github.com/luben/zstd-jni/compare/master...mkoncek:internal-headers2

[luben]

Your suggestion looks good for me. I think there will be warnings if explicit casts are needed.

[mkoncek]

Good, I will double-check if I understand the rules of integer casts correctly and that I am not changing behaviour.

[mkoncek]

Point 2 and 3: https://www.iso-9899.info/n1570.html#6.3.1.3 signed -> unsigned is well defined, unsigned -> signed is implementation-defined. While I was in favor of using only signed types in those functions, ZSTD library functions return size_t whereas JNI bindings often return signed types. Therefore there is no way around implementation-defined behaviour. So my suggested patch is probably the best approach with no further modifications to types used inside JNI functions.

[mkoncek]

I rebased this PR to the suggested one.

[luben]

Merged. Thanks for the contribution!