Add check module.

Author: nemequ

README.md

@@ -35,7 +35,7 @@ Currently ready-to-use modules include:
  * [clock](https://github.com/nemequ/portable-snippets/tree/master/clock) —
    cross-platform wall clock, CPU time, and monotonic time
 
-There are also modules which are not yet ready for widespread use, but
+There are also modules which may not yet be ready for widespread use, but
 would benefit greatly from testing:
 
  * [unaligned](https://github.com/nemequ/portable-snippets/tree/master/unaligned) —
@@ -46,6 +46,8 @@ would benefit greatly from testing:
    random number generation (3 flavors: cryptographic, reproducible, and fast)
  * [debug-trap](https://github.com/nemequ/portable-snippets/tree/master/debug-trap) —
    debugging traps and assertions
+ * [check](https://github.com/nemequ/portable-snippets/tree/master/check) —
+   assertion checking
 
 Modules can be used in isolation, though some do work better together,
 so if you can keep the whole repository together instead of just

check/README.md

@@ -0,0 +1,38 @@
+# Assertion Checking
+
+This module provide a variety of assert()-style macros.  Unlike the
+standard `assert()` macro from `<assert.h>`, most of these macros are
+typed so the input values can be propogated to the string output on
+failure.
+
+For documentation, µnit offers very similar macros (this module was
+originally based off of the macros from µnit), most of
+[the documentation for them](https://nemequ.github.io/munit/#assertions)
+applies to this module's macros, just substitute the `munit_` namespace
+with `psnip_`.
+
+Additionally, unless you define `PSNIP_CHECK_FAIL_DEFINED`, a failing
+assertion will considered undefined behavior even when `NDEBUG` is
+defined.  This allows the compiler to perform optimizations which
+would not otherwise be possible.
+
+## Dependencies
+
+To maximize portability you should #include the exact-int module
+before including check.h, but if you don't want to add the extra
+file to your project you can omit it and this module will simply rely
+on <stdint.h>.  As an alternative you may define the following macros
+to appropriate values yourself:
+
+ * `psnip_int8_t`
+ * `psnip_uint8_t`
+ * `psnip_int16_t`
+ * `psnip_uint16_t`
+ * `psnip_int32_t`
+ * `psnip_uint32_t`
+ * `psnip_int64_t`
+ * `psnip_uint64_t`
+
+Including [Hedley](https://nemequ.github.io/hedley/) before check.h
+will significantly improve compiler support and may improve
+performance.