Minimize the scope of the |BN_*_SIZE_*| constants.

mul.c is the only file that uses these values.

Change-Id: I50a685cbff0f26357229e742f42e014434e9cebe
Reviewed-on: https://boringssl-review.googlesource.com/7061
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/bn/internal.h b/crypto/bn/internal.h
index 7ee94fc..cb57bb4 100644
--- a/crypto/bn/internal.h
+++ b/crypto/bn/internal.h
@@ -181,12 +181,6 @@
 #endif
 
 
-/* Pentium pro 16,16,16,32,64 */
-/* Alpha       16,16,16,16.64 */
-#define BN_MULL_SIZE_NORMAL (16)              /* 32 */
-#define BN_MUL_RECURSIVE_SIZE_NORMAL (16)     /* 32 less than */
-#define BN_SQR_RECURSIVE_SIZE_NORMAL (16)     /* 32 */
-
 #define STATIC_BIGNUM(x)                                \
   {                                                     \
     (BN_ULONG *)x, sizeof(x) / sizeof(BN_ULONG),        \
diff --git a/crypto/bn/mul.c b/crypto/bn/mul.c
index 84dc24c..d2d8fd8 100644
--- a/crypto/bn/mul.c
+++ b/crypto/bn/mul.c
@@ -62,6 +62,10 @@
 #include "internal.h"
 
 
+#define BN_MUL_RECURSIVE_SIZE_NORMAL 16
+#define BN_SQR_RECURSIVE_SIZE_NORMAL BN_MUL_RECURSIVE_SIZE_NORMAL
+
+
 void bn_mul_normal(BN_ULONG *r, BN_ULONG *a, int na, BN_ULONG *b, int nb) {
   BN_ULONG *rr;
 
@@ -593,7 +597,8 @@
     }
   }
 
-  if ((al >= BN_MULL_SIZE_NORMAL) && (bl >= BN_MULL_SIZE_NORMAL)) {
+  static const int kMulNormalSize = 16;
+  if (al >= kMulNormalSize && bl >= kMulNormalSize) {
     if (i >= -1 && i <= 1) {
       /* Find out the power of two lower or equal
          to the longest of the two numbers */