Compiling Hush basics

doc/developer-notes.md

@@ -1,3 +1,53 @@
+# Basics
+
+First the basics, how to compile code in this repo.
+
+First you will want to clone the code locally:
+
+```
+git clone https://git.hush.is/hush/hush3
+cd hush3
+```
+
+If you want to compile a branch other than master (the default), such as
+our development tip (the `dev` branch) you can switch to it:
+
+```
+git checkout dev
+```
+
+Then install needed dependencies. This is different on each OS as well as
+older or newer systems. See https://git.hush.is/hush/hush3/src/branch/dev/INSTALL.md for
+details on installing dependencies. If you are using a recent-ish Linux distro, this
+is probably what you need:
+
+```
+# install build dependencies
+sudo apt-get install build-essential pkg-config libc6-dev m4 g++-multilib \
+      autoconf libtool ncurses-dev unzip git zlib1g-dev wget \
+      bsdmainutils automake curl unzip nano libsodium-dev cmake
+```
+
+Finally to compile the software you use `./build.sh` . It is quite slow
+to only use a single thread, so you can use multiple threads, for example 4,
+like this:
+
+```
+./build.sh -j4
+```
+
+Each `build.sh` thread will take ~2GB of RAM so beware of that. If you have
+compiled before and just made a change to C++ code, you can probably use
+`make` instead and use a high number of threads. For example, if your CPU
+has 8 physical cores and 16 "virtual cores" then you can use `make -j16` and
+things will compile much faster. Each `make` threads takes only about 200MB of RAM.
+If `make` fails in a weird way complaining about Makefiles, you probably need to
+run `build.sh`, which takes care of regenerating Makefiles and installing some
+additional dependencies.
+
+Sometimes using multiple threads the build can fail, so if it does, try again
+with a different number of threads or just one thread before reporting an issue.
+
 # Fresh sync
 
 Many times, you will want to do a "fresh sync" test, to verify code works when syncing from the genesis block, which is a different code path than a "partial sync" which means you already have part of blockchain history and are "catching up" to get in sync.