* nix-hash: option `--truncate' to truncate the hash to 160 bits. Hmm,

  kind of ad hoc ;-)

2 files changed, 4 insertions, 0 deletions

diff --git a/src/nix-hash/help.txt b/src/nix-hash/help.txt
index 31fff1ffabd6..082cc7571c06 100644
--- a/src/nix-hash/help.txt
+++ b/src/nix-hash/help.txt
@@ -6,3 +6,4 @@ files.
   --flat: compute hash of regular file contents, not metadata
   --base32: print hash in base-32 instead of hexadecimal
   --type HASH: use hash algorithm HASH ("md5" (default), "sha1", "sha256")
+  --truncate: truncate the hash to 160 bits
diff --git a/src/nix-hash/nix-hash.cc b/src/nix-hash/nix-hash.cc
index 78c6f44012b4..4a7c943963d9 100644
--- a/src/nix-hash/nix-hash.cc
+++ b/src/nix-hash/nix-hash.cc
@@ -16,12 +16,14 @@ void run(Strings args)
     HashType ht = htMD5;
     bool flat = false;
     bool base32 = false;
+    bool truncate = false;
     
     for (Strings::iterator i = args.begin();
          i != args.end(); i++)
     {
         if (*i == "--flat") flat = true;
         else if (*i == "--base32") base32 = true;
+        else if (*i == "--truncate") truncate = true;
         else if (*i == "--type") {
             ++i;
             if (i == args.end()) throw UsageError("`--type' requires an argument");
@@ -31,6 +33,7 @@ void run(Strings args)
         }
         else {
             Hash h = flat ? hashFile(ht, *i) : hashPath(ht, *i);
+            if (truncate && h.hashSize > 20) h = compressHash(h, 20);
             cout << format("%1%\n") %
                 (base32 ? printHash32(h) : printHash(h));
         }