guix gc: Adjust size suffix based on the amount of data.

* guix/ui.scm (number->size): New procedure.
* guix/scripts/gc.scm (guix-gc)[actions]: Display the amount of
collected-garbage using more specific units.
[ensure-free-space]: Display the size using an appropriate size unit.
* nix/libstore/gc.cc (deletePathRecursive, removeUnusedLinks): Same.
* nix/libstore/optimise-store.cc (showBytes): Move function ...
* nix/libstore/misc.cc: ... to here.  Expand to adjust the output based
on the amount of bytes received.

Change-Id: Idceb1a13f8e45f959d327f53d1a8accb29d2678b

4 files changed, 26 insertions, 9 deletions

diff --git a/nix/libstore/gc.cc b/nix/libstore/gc.cc
index 1766a684122..08638b51153 100644
--- a/nix/libstore/gc.cc
+++ b/nix/libstore/gc.cc
@@ -433,8 +433,7 @@ void LocalStore::deletePathRecursive(GCState & state, const Path & path)
         printMsg(lvlInfo, format("[%1%%%] deleting '%2%'") % percentage % path);
     } else {
         auto freed = state.results.bytesFreed + state.bytesInvalidated;
-        freed /=  1024ULL * 1024ULL;
-        printMsg(lvlInfo, format("[%1% MiB] deleting '%2%'") % freed % path);
+        printMsg(lvlInfo, format("[%1%] deleting '%2%'") % showBytes(freed) % path);
     }
 
     state.results.paths.insert(path);
@@ -629,9 +628,9 @@ void LocalStore::removeUnusedLinks(const GCState & state)
     if (stat(linksDir.c_str(), &st) == -1)
         throw SysError(format("statting `%1%'") % linksDir);
     long long overhead = st.st_size;
+    long long freedbytes = (unsharedSize - actualSize - overhead);
 
-    printMsg(lvlInfo, format("note: currently hard linking saves %.2f MiB")
-        % ((unsharedSize - actualSize - overhead) / (1024.0 * 1024.0)));
+    printMsg(lvlInfo, format("note: currently hard linking saves %1%") % showBytes(freedbytes));
 }
 
 
diff --git a/nix/libstore/misc.cc b/nix/libstore/misc.cc
index bc5dec88bf2..e9904f3c4f4 100644
--- a/nix/libstore/misc.cc
+++ b/nix/libstore/misc.cc
@@ -1,4 +1,5 @@
 #include "misc.hh"
+#include <math.h>
 #include "store-api.hh"
 #include "local-store.hh"
 #include "globals.hh"
@@ -94,5 +95,25 @@ Paths topoSortPaths(StoreAPI & store, const PathSet & paths)
     return sorted;
 }
 
+/* Max of LLONG_MAX is 8 EiB */
+string showBytes(long long bytes)
+{
+    if (llabs(bytes > exp2l(60))) {
+        return (format("%7.2f EiB") % (bytes / exp2l(60))).str();
+    } else if (llabs(bytes > exp2l(50))) {
+        return (format("%7.2f PiB") % (bytes / exp2l(50))).str();
+    } else if (llabs(bytes > exp2l(40))) {
+        return (format("%7.2f TiB") % (bytes / exp2l(40))).str();
+    } else if (llabs(bytes > exp2l(30))) {
+        return (format("%7.2f GiB") % (bytes / exp2l(30))).str();
+    } else if (llabs(bytes > exp2l(20))) {
+        return (format("%7.2f MiB") % (bytes / exp2l(20))).str();
+    } else if (llabs(bytes > exp2l(10))) {
+        return (format("%7.2f KiB") % (bytes / exp2l(10))).str();
+    } else {
+        return (format("%4f  bytes") % bytes).str();
+    }
+}
+
 
 }
diff --git a/nix/libstore/misc.hh b/nix/libstore/misc.hh
index f70cda9fd0c..1d36ccf9dce 100644
--- a/nix/libstore/misc.hh
+++ b/nix/libstore/misc.hh
@@ -25,5 +25,6 @@ bool willBuildLocally(const Derivation & drv);
 
 bool substitutesAllowed(const Derivation & drv);
 
+string showBytes(long long bytes);
 
 }
diff --git a/nix/libstore/optimise-store.cc b/nix/libstore/optimise-store.cc
index 8d5bf28da9d..e17d9160d6c 100644
--- a/nix/libstore/optimise-store.cc
+++ b/nix/libstore/optimise-store.cc
@@ -1,5 +1,6 @@
 #include "config.h"
 
+#include "misc.hh"
 #include "util.hh"
 #include "local-store.hh"
 #include "globals.hh"
@@ -252,11 +253,6 @@ void LocalStore::optimiseStore(OptimiseStats & stats)
     }
 }
 
-static string showBytes(unsigned long long bytes)
-{
-    return (format("%.2f MiB") % (bytes / (1024.0 * 1024.0))).str();
-}
-
 void LocalStore::optimiseStore()
 {
     OptimiseStats stats;