Issue #16686: Fixed a lot of bugs in audioop module.

* avgpp() and maxpp() no more crash on empty and 1-samples input fragment. They now work when peak-peak values are greater INT_MAX.
* ratecv() no more crashes on empty input fragment.
* Fixed an integer overflow in ratecv().
* Fixed an integer overflow in add() and bias() for 32-bit samples.
* reverse(), lin2lin() and ratecv() no more lose precision for 32-bit samples.
* max() and rms() no more returns negative result for 32-bit sample -0x80000000.
* minmax() now returns correct max value for 32-bit sample -0x80000000.
* avg(), mul(), tomono() and tostereo() now round negative result down and can return 32-bit sample -0x80000000.
* add() now can return 32-bit sample -0x80000000.

Doc/library/audioop.rst

@@ -36,7 +36,7 @@ The module defines the following variables and functions:
 
    Return a fragment which is the addition of the two samples passed as parameters.
    *width* is the sample width in bytes, either ``1``, ``2`` or ``4``.  Both
-   fragments should have the same length.
+   fragments should have the same length.  Samples are truncated in case of overflow.
 
 
 .. function:: adpcm2lin(adpcmfragment, width, state)
@@ -67,7 +67,7 @@ The module defines the following variables and functions:
 .. function:: bias(fragment, width, bias)
 
    Return a fragment that is the original fragment with a bias added to each
-   sample.
+   sample.  Samples wrap around in case of overflow.
 
 
 .. function:: cross(fragment, width)
@@ -175,7 +175,7 @@ The module defines the following variables and functions:
 .. function:: mul(fragment, width, factor)
 
    Return a fragment that has all samples in the original fragment multiplied by
-   the floating-point value *factor*.  Overflow is silently ignored.
+   the floating-point value *factor*.  Samples are truncated in case of overflow.
 
 
 .. function:: ratecv(fragment, width, nchannels, inrate, outrate, state[, weightA[, weightB]])

Misc/NEWS

@@ -215,6 +215,12 @@ Core and Builtins
 Library
 -------
 
+- Issue #16686: Fixed a lot of bugs in audioop module.  Fixed crashes in
+  avgpp(), maxpp() and ratecv().  Fixed an integer overflow in add(), bias(),
+  and ratecv().  reverse(), lin2lin() and ratecv() no more lose precision for
+  32-bit samples.  max() and rms() no more returns a negative result and
+  various other functions now work correctly with 32-bit sample -0x80000000.
+
 - Issue #17073: Fix some integer overflows in sqlite3 module.
 
 - Issue #17114: IDLE now uses non-strict config parser.