From 79d8c4cab327a7cd5879a0508f6498d6d6533399 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 23 Nov 2016 20:45:54 -0800
Subject: Adding clearhash function.

This is needed for an upcoming bugfix, so why not expose it as
an intrinsic.

* hash.c (clearhash): New function.
(hash_init): clearhash intrinsic registered.

* hash.h (clearhash): Declared.

* txr.1: Documented clearhash.
---
 hash.c | 13 +++++++++++++
 hash.h |  1 +
 txr.1  | 21 +++++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/hash.c b/hash.c
index b2bbe0ec..a786a9c6 100644
--- a/hash.c
+++ b/hash.c
@@ -754,6 +754,18 @@ val remhash(val hash, val key)
   return nil;
 }
 
+val clearhash(val hash)
+{
+  struct hash *h = coerce(struct hash *, cobj_handle(hash, hash_s));
+  val mod = num_fast(256);
+  val table = vector(mod, nil);
+  cnum oldcount = h->count;
+  h->modulus = c_num(mod);
+  h->count = 0;
+  h->table = table;
+  return oldcount ? num(oldcount) : nil;
+}
+
 val hash_count(val hash)
 {
   struct hash *h = coerce(struct hash *, cobj_handle(hash, hash_s));
@@ -1374,6 +1386,7 @@ void hash_init(void)
   reg_fun(intern(lit("sethash"), user_package), func_n3(sethash));
   reg_fun(intern(lit("pushhash"), user_package), func_n3(pushhash));
   reg_fun(intern(lit("remhash"), user_package), func_n2(remhash));
+  reg_fun(intern(lit("clearhash"), user_package), func_n1(clearhash));
   reg_fun(intern(lit("hash-count"), user_package), func_n1(hash_count));
   reg_fun(intern(lit("get-hash-userdata"), user_package), ghu);
   reg_fun(intern(lit("hash-userdata"), user_package), ghu);
diff --git a/hash.h b/hash.h
index a0c40797..0f0db6df 100644
--- a/hash.h
+++ b/hash.h
@@ -39,6 +39,7 @@ val gethash_f(val hash, val key, loc found);
 val sethash(val hash, val key, val value);
 val pushhash(val hash, val key, val value);
 val remhash(val hash, val key);
+val clearhash(val hash);
 val hash_count(val hash);
 val get_hash_userdata(val hash);
 val set_hash_userdata(val hash, val data);
diff --git a/txr.1 b/txr.1
index 2effcf39..9376d51a 100644
--- a/txr.1
+++ b/txr.1
@@ -34998,6 +34998,27 @@ is returned. Otherwise
 .code nil
 is returned.
 
+.coNP Function @ clearhash
+.synb
+.mets (clearhash << hash )
+.syne
+.desc
+The
+.code clearhash
+function removes all keys-value pairs from
+.metn hash ,
+causing it to be empty.
+
+If
+.meta hash
+is already empty prior to the operation, then
+.codn nil ,
+is returned.
+
+Otherwise an integer is returned indicating the number of entries
+that were purged from
+.metn hash .
+
 .coNP Function @ hash-count
 .synb
 .mets (hash-count << hash )
-- 
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