I stumbled upon this while debugging a strange issue with stream_socket_client() where it randomly throws out errors when the connection timeout is set to below 1s. The logic to calculate time difference in php_openssl_subtract_timeval() is wrong when a.tv_usec < b.tv_usec, causing connection errors before the timeout is reached.

I have created a script to reproduce the issue - https://gist.github.com/joec4i/ef1b1156ed79e23487400c68a5f693cb

Before the patch

$ php socket_test.php 2000 0.9 | grep error
failed in 0.0037751197814941s, error.no=0, errstr=
failed in 0.0031719207763672s, error.no=0, errstr=
failed in 0.0026381015777588s, error.no=0, errstr=
failed in 0.0029230117797852s, error.no=0, errstr=
failed in 0.0027728080749512s, error.no=0, errstr=
Tested 2000 connections(timeout=0.9) with in 6.1318738460541s with 5 errors

The number of errors may vary but as you can see, connection failures happened way before the 0.9s timeout.

After the patch

$ php socket_test.php 10000 0.1 | grep error
Tested 10000 connections(timeout=0.1) with in 28.441427946091s with 0 errors

Please review. Thanks!