openblas: downgrade to 0.2.12, build generic target

pkgs/development/libraries/science/math/openblas/default.nix

@@ -1,47 +1,40 @@
 { stdenv, fetchurl, gfortran, perl, liblapack, config }:
 
-# Minimum CPU requirements:
-# x86: Pentium 4 (Prescott, circa 2004)
-# x86_64: Opteron (circa 2003)
-# These are the settings used for the generic builds. Performance will
-# be poor on modern systems. The goal of the Hydra builds is simply to
-# support as many systems as possible. OpenBLAS may support older
-# CPU architectures, but you will need to set 'config.openblas.target'
-# and 'config.openblas.preferLocalBuild', which will build it on your
-# local machine.
+with stdenv.lib;
 
 let local = config.openblas.preferLocalBuild or false;
-    localTarget = config.openblas.target or "";
+    genericFlags =
+      [
+        "DYNAMIC_ARCH=1"
+        "TARGET=GENERIC"
+        "NUM_THREADS=64"
+      ];
+    localFlags = config.openblas.flags or
+      optionals (hasAttr "target" config.openblas) [ "TARGET=${config.openblas.target}" ];
 in
 stdenv.mkDerivation rec {
-  version = "0.2.13";
+  version = "0.2.12";
 
   name = "openblas-${version}";
   src = fetchurl {
     url = "https://github.com/xianyi/OpenBLAS/tarball/v${version}";
-    sha256 = "1asg5mix13ipxgj5h2yj2p0r8km1di5jbcjkn5gmhb37nx7qfv6k";
+    sha256 = "0389dnybfvag8zms5w1xlwcknq2l2am1vcfssjkax49r1rq2f5qg";
     name = "openblas-${version}.tar.gz";
   };
 
   preBuild = "cp ${liblapack.src} lapack-${liblapack.meta.version}.tgz";
 
-  buildInputs = [gfortran perl];
+  nativeBuildInputs = [gfortran perl];
 
-  cpu = builtins.head (stdenv.lib.splitString "-" stdenv.system);
-
-  target = if local then localTarget else
-    if cpu == "i686" then "PRESCOTT" else
-    if cpu == "x86_64" then "OPTERON" else
-     # allow autodetect
-      "";
-
-  makeFlags = [
-    "${if target != "" then "TARGET=" else ""}${target}"
-    "FC=gfortran"
-    "CC=gcc"
-    ''PREFIX="''$(out)"''
-    "INTERFACE64=1"
-  ];
+  makeFlags =
+    (if local then localFlags else genericFlags)
+    ++
+    [
+      "FC=gfortran"
+      "CC=gcc"
+      ''PREFIX="''$(out)"''
+      "INTERFACE64=1"
+    ];
 
   meta = with stdenv.lib; {
     description = "Basic Linear Algebra Subprograms";