Move |bn_div_words| to crypto/bn/div.c and make it static.

It is only used by |bn_div_rem_words|.

Change-Id: I57627091d8db5890d7fea34d8560897717008646
Reviewed-on: https://boringssl-review.googlesource.com/7128
Reviewed-by: David Benjamin <davidben@google.com>

crypto/bn/div.c

@@ -56,12 +56,86 @@
 
 #include <openssl/bn.h>
 
+#include <assert.h>
 #include <limits.h>
 #include <openssl/err.h>
 
 #include "internal.h"
 
 
+#if !defined(BN_ULLONG)
+/* bn_div_words divides a double-width |h|,|l| by |d| and returns the result,
+ * which must fit in a |BN_ULONG|. */
+static BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d) {
+  BN_ULONG dh, dl, q, ret = 0, th, tl, t;
+  int i, count = 2;
+
+  if (d == 0) {
+    return BN_MASK2;
+  }
+
+  i = BN_num_bits_word(d);
+  assert((i == BN_BITS2) || (h <= (BN_ULONG)1 << i));
+
+  i = BN_BITS2 - i;
+  if (h >= d) {
+    h -= d;
+  }
+
+  if (i) {
+    d <<= i;
+    h = (h << i) | (l >> (BN_BITS2 - i));
+    l <<= i;
+  }
+  dh = (d & BN_MASK2h) >> BN_BITS4;
+  dl = (d & BN_MASK2l);
+  for (;;) {
+    if ((h >> BN_BITS4) == dh) {
+      q = BN_MASK2l;
+    } else {
+      q = h / dh;
+    }
+
+    th = q * dh;
+    tl = dl * q;
+    for (;;) {
+      t = h - th;
+      if ((t & BN_MASK2h) ||
+          ((tl) <= ((t << BN_BITS4) | ((l & BN_MASK2h) >> BN_BITS4)))) {
+        break;
+      }
+      q--;
+      th -= dh;
+      tl -= dl;
+    }
+    t = (tl >> BN_BITS4);
+    tl = (tl << BN_BITS4) & BN_MASK2h;
+    th += t;
+
+    if (l < tl) {
+      th++;
+    }
+    l -= tl;
+    if (h < th) {
+      h += d;
+      q--;
+    }
+    h -= th;
+
+    if (--count == 0) {
+      break;
+    }
+
+    ret = q << BN_BITS4;
+    h = ((h << BN_BITS4) | (l >> BN_BITS4)) & BN_MASK2;
+    l = (l & BN_MASK2l) << BN_BITS4;
+  }
+
+  ret |= q;
+  return ret;
+}
+#endif /* !defined(BN_ULLONG) */
+
 static inline void bn_div_rem_words(BN_ULONG *quotient_out, BN_ULONG *rem_out,
                                     BN_ULONG n0, BN_ULONG n1, BN_ULONG d0) {
   /* GCC and Clang generate function calls to |__udivdi3| and |__umoddi3| when

crypto/bn/generic.c

@@ -202,80 +202,6 @@ void bn_sqr_words(BN_ULONG *r, const BN_ULONG *a, int n) {
   }
 }
 
-#if !defined(BN_ULLONG)
-
-/* Divide h,l by d and return the result. */
-BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d) {
-  BN_ULONG dh, dl, q, ret = 0, th, tl, t;
-  int i, count = 2;
-
-  if (d == 0) {
-    return BN_MASK2;
-  }
-
-  i = BN_num_bits_word(d);
-  assert((i == BN_BITS2) || (h <= (BN_ULONG)1 << i));
-
-  i = BN_BITS2 - i;
-  if (h >= d) {
-    h -= d;
-  }
-
-  if (i) {
-    d <<= i;
-    h = (h << i) | (l >> (BN_BITS2 - i));
-    l <<= i;
-  }
-  dh = (d & BN_MASK2h) >> BN_BITS4;
-  dl = (d & BN_MASK2l);
-  for (;;) {
-    if ((h >> BN_BITS4) == dh) {
-      q = BN_MASK2l;
-    } else {
-      q = h / dh;
-    }
-
-    th = q * dh;
-    tl = dl * q;
-    for (;;) {
-      t = h - th;
-      if ((t & BN_MASK2h) ||
-          ((tl) <= ((t << BN_BITS4) | ((l & BN_MASK2h) >> BN_BITS4)))) {
-        break;
-      }
-      q--;
-      th -= dh;
-      tl -= dl;
-    }
-    t = (tl >> BN_BITS4);
-    tl = (tl << BN_BITS4) & BN_MASK2h;
-    th += t;
-
-    if (l < tl) {
-      th++;
-    }
-    l -= tl;
-    if (h < th) {
-      h += d;
-      q--;
-    }
-    h -= th;
-
-    if (--count == 0) {
-      break;
-    }
-
-    ret = q << BN_BITS4;
-    h = ((h << BN_BITS4) | (l >> BN_BITS4)) & BN_MASK2;
-    l = (l & BN_MASK2l) << BN_BITS4;
-  }
-
-  ret |= q;
-  return ret;
-}
-
-#endif /* !defined(BN_ULLONG) */
-
 #ifdef BN_ULLONG
 BN_ULONG bn_add_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
                       int n) {

crypto/bn/internal.h

@@ -224,10 +224,6 @@ int bn_mul_mont(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,
 #error "Either BN_ULLONG or BN_UMULT_LOHI must be defined on every platform."
 #endif
 
-#if !defined(BN_ULLONG)
-BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d);
-#endif
-
 
 #if defined(__cplusplus)
 }  /* extern C */