diff --git a/ChangeLog b/ChangeLog
index ec8398093..2fc01debd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2012-04-07  Vladimir Serbinenko  <phcoder@gmail.com>
+
+	* grub-core/lib/adler32.c: Recode due to license unclearness.
+
 2012-04-07  Vladimir Serbinenko  <phcoder@gmail.com>
 
 	* grub-core/io/lzopio.c (read_block_header): Fix incorrect byte swapping
diff --git a/grub-core/lib/adler32.c b/grub-core/lib/adler32.c
index 2a2464db3..43b68af62 100644
--- a/grub-core/lib/adler32.c
+++ b/grub-core/lib/adler32.c
@@ -1,7 +1,6 @@
-/* adler32.c - adler32 check.  */
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 2011  Free Software Foundation, Inc.
+ *  Copyright (C) 2012  Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -17,117 +16,50 @@
  *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <grub/types.h>
+
 #include <grub/dl.h>
 #include <grub/crypto.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
-/* Based on adler32() from adler32.c of zlib-1.2.5 library. */
-
-#define BASE 65521UL
-#define NMAX 5552
-
-#define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
-#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
-#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
-#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
-#define DO16(buf)   DO8(buf,0); DO8(buf,8);
-
-static grub_uint32_t
-update_adler32 (grub_uint32_t adler, const grub_uint8_t *buf, grub_size_t len)
+struct adler32_context
 {
-  unsigned long sum2;
-  unsigned int n;
-
-  sum2 = (adler >> 16) & 0xffff;
-  adler &= 0xffff;
-
-  if (len == 1)
-    {
-      adler += buf[0];
-      if (adler >= BASE)
-	adler -= BASE;
-      sum2 += adler;
-      if (sum2 >= BASE)
-	sum2 -= BASE;
-      return adler | (sum2 << 16);
-    }
-
-  if (len < 16)
-    {
-      while (len--)
-	{
-	  adler += *buf++;
-	  sum2 += adler;
-	}
-      if (adler >= BASE)
-	adler -= BASE;
-      sum2 %= BASE;
-      return adler | (sum2 << 16);
-    }
-
-  while (len >= NMAX)
-    {
-      len -= NMAX;
-      n = NMAX / 16;
-      do
-	{
-	  DO16 (buf);
-	  buf += 16;
-	}
-      while (--n);
-      adler %= BASE;
-      sum2 %= BASE;
-    }
-
-  if (len)
-    {
-      while (len >= 16)
-	{
-	  len -= 16;
-	  DO16 (buf);
-	  buf += 16;
-	}
-      while (len--)
-	{
-	  adler += *buf++;
-	  sum2 += adler;
-	}
-      adler %= BASE;
-      sum2 %= BASE;
-    }
-
-  return adler | (sum2 << 16);
-}
-
-typedef struct
-{
-  grub_uint32_t adler;
-}
-adler32_context;
+  grub_uint16_t a, b;
+  grub_uint32_t c;
+};
 
 static void
 adler32_init (void *context)
 {
-  adler32_context *ctx = (adler32_context *) context;
-  ctx->adler = 1;
+  struct adler32_context *ctx = context;
+
+  ctx->a = 1;
+  ctx->b = 0;
+}
+
+#define MOD 65521
+
+static grub_uint16_t
+mod_add (grub_uint16_t a, grub_uint16_t b)
+{
+  if ((grub_uint32_t) a + (grub_uint32_t) b >= MOD)
+    return a + b - MOD;
+  return a + b;
 }
 
 static void
 adler32_write (void *context, const void *inbuf, grub_size_t inlen)
 {
-  adler32_context *ctx = (adler32_context *) context;
-  if (!inbuf)
-    return;
-  ctx->adler = update_adler32 (ctx->adler, inbuf, inlen);
-}
+  struct adler32_context *ctx = context;
+  const grub_uint8_t *ptr = inbuf;
 
-static grub_uint8_t *
-adler32_read (void *context)
-{
-  adler32_context *ctx = (adler32_context *) context;
-  return (grub_uint8_t *) &ctx->adler;
+  while (inlen)
+    {
+      ctx->a = mod_add (ctx->a, *ptr);
+      ctx->b = mod_add (ctx->a, ctx->b);
+      inlen--;
+      ptr++;
+    }
 }
 
 static void
@@ -135,19 +67,36 @@ adler32_final (void *context __attribute__ ((unused)))
 {
 }
 
-gcry_md_spec_t _gcry_digest_spec_adler32 = {
-  "ADLER32",0 , 0, 0 , 4,
-  adler32_init, adler32_write, adler32_final, adler32_read,
-  sizeof (adler32_context),
-  .blocksize = 64
-};
+static grub_uint8_t *
+adler32_read (void *context)
+{
+  struct adler32_context *ctx = context;
+  if (ctx->a > MOD)
+    ctx->a -= MOD;
+  if (ctx->b > MOD)
+    ctx->b -= MOD;
+  ctx->c = grub_cpu_to_be32 (ctx->a | (ctx->b << 16));
+  return (grub_uint8_t *) &ctx->c;
+}
+
+static gcry_md_spec_t spec_adler32 =
+  {
+    "ADLER32", 0, 0, 0, 4,
+    adler32_init, adler32_write, adler32_final, adler32_read,
+    sizeof (struct adler32_context),
+#ifdef GRUB_UTIL
+    .modname = "adler32",
+#endif
+    .blocksize = 64
+  };
+
 
 GRUB_MOD_INIT(adler32)
 {
-  grub_md_register (&_gcry_digest_spec_adler32);
+  grub_md_register (&spec_adler32);
 }
 
 GRUB_MOD_FINI(adler32)
 {
-  grub_md_unregister (&_gcry_digest_spec_adler32);
+  grub_md_unregister (&spec_adler32);
 }