* bignum.c (bary_pack): Specialized packers implemented.

(HOST_BIGENDIAN_P): New macro.
  (ALIGNOF): New macro.
  (CLEAR_LOWBITS): New macro.
  (FILL_LOWBITS): New macro.
  (swap_bdigit): New macro.
  (bary_2comp): Returns an int.

* internal.h (swap16): Moved from pack.c
  (swap32): Ditto.
  (swap64): Ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41544 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,17 @@
+Sat Jun 22 02:18:07 2013  Tanaka Akira  <akr@fsij.org>
+
+	* bignum.c (bary_pack): Specialized packers implemented.
+	  (HOST_BIGENDIAN_P): New macro.
+	  (ALIGNOF): New macro.
+	  (CLEAR_LOWBITS): New macro.
+	  (FILL_LOWBITS): New macro.
+	  (swap_bdigit): New macro.
+	  (bary_2comp): Returns an int.
+
+	* internal.h (swap16): Moved from pack.c
+	  (swap32): Ditto.
+	  (swap64): Ditto.
+
 Fri Jun 21 21:29:49 2013  Masaya Tarui  <tarui@ruby-lang.org>
 
 	* gc.c (typedef enum): Introduce flags of major gc reason.

bignum.c

@@ -33,6 +33,15 @@ static VALUE big_three = Qnil;
 #define USHORT _USHORT
 #endif
 
+#ifdef WORDS_BIGENDIAN
+#   define HOST_BIGENDIAN_P 1
+#else
+#   define HOST_BIGENDIAN_P 0
+#endif
+#define ALIGNOF(type) ((int)offsetof(struct { char f1; type f2; }, f2))
+#define CLEAR_LOWBITS(d, numbits) (sizeof(d) * CHAR_BIT <= (numbits) ? 0 : ((d) >> (numbits)) << (numbits))
+#define FILL_LOWBITS(d, numbits) (sizeof(d) * CHAR_BIT <= (numbits) ? ~((d)*0) : (d) | ((((d)*0+1) << (numbits))-1))
+
 #define BDIGITS(x) (RBIGNUM_DIGITS(x))
 #define BITSPERDIG (SIZEOF_BDIGITS*CHAR_BIT)
 #define BIGRAD ((BDIGIT_DBL)1 << BITSPERDIG)
@@ -48,6 +57,14 @@ static VALUE big_three = Qnil;
 #define BIGLO(x) ((BDIGIT)((x) & BDIGMAX))
 #define BDIGMAX ((BDIGIT)(BIGRAD-1))
 
+#if SIZEOF_BDIGITS == 2
+#   define swap_bdigit(x) swap16(x)
+#elif SIZEOF_BDIGITS == 4
+#   define swap_bdigit(x) swap32(x)
+#elif SIZEOF_BDIGITS == 8
+#   define swap_bdigit(x) swap64(x)
+#endif
+
 #define BIGZEROP(x) (RBIGNUM_LEN(x) == 0 || \
 		     (BDIGITS(x)[0] == 0 && \
 		      (RBIGNUM_LEN(x) == 1 || bigzero_p(x))))
@@ -76,7 +93,7 @@ static void bary_sub(BDIGIT *zds, size_t zn, BDIGIT *xds, size_t xn, BDIGIT *yds
 static void bary_divmod(BDIGIT *qds, size_t nq, BDIGIT *rds, size_t nr, BDIGIT *xds, size_t nx, BDIGIT *yds, size_t ny);
 static void bary_add(BDIGIT *zds, size_t zn, BDIGIT *xds, size_t xn, BDIGIT *yds, size_t yn);
 static int bary_pack(int sign, BDIGIT *ds, size_t num_bdigits, void *words, size_t numwords, size_t wordsize, size_t nails, int flags);
-static BDIGIT bary_2comp(BDIGIT *ds, size_t n);
+static int bary_2comp(BDIGIT *ds, size_t n);
 
 #define BIGNUM_DEBUG 0
 #if BIGNUM_DEBUG
@@ -231,7 +248,7 @@ rb_big_clone(VALUE x)
     return z;
 }
 
-static BDIGIT
+static int
 bary_2comp(BDIGIT *ds, size_t n)
 {
     size_t i = n;
@@ -244,7 +261,7 @@ bary_2comp(BDIGIT *ds, size_t n)
 	ds[i++] = BIGLO(num);
 	num = BIGDN(num);
     } while (i < n);
-    return (BDIGIT)num;
+    return num != 0;
 }
 
 /* modify a bignum by 2's complement */
@@ -901,6 +918,170 @@ bary_pack(int sign, BDIGIT *ds, size_t num_bdigits, void *words, size_t numwords
         sign = 0;
     }
 
+    if (nails == 0 && sign == 0) {
+        MEMZERO(words, unsigned char, numwords * wordsize);
+        return 0;
+    }
+    if (nails == 0 && numwords == 1) {
+        int need_swap = wordsize != 1 &&
+            (flags & INTEGER_PACK_BYTEORDER_MASK) != INTEGER_PACK_NATIVE_BYTE_ORDER &&
+            ((flags & INTEGER_PACK_MSBYTE_FIRST) ? !HOST_BIGENDIAN_P : HOST_BIGENDIAN_P);
+        if (0 < sign || !(flags & INTEGER_PACK_2COMP)) {
+            BDIGIT d;
+            if (wordsize == 1) {
+                *((unsigned char *)words) = (unsigned char)(d = dp[0]);
+                return ((1 < de - dp || CLEAR_LOWBITS(d, 8) != 0) ? 2 : 1) * sign;
+            }
+#if defined(HAVE_UINT16_T) && 2 <= SIZEOF_BDIGITS
+            if (wordsize == 2 && (uintptr_t)words % ALIGNOF(uint16_t) == 0) {
+                uint16_t u = (uint16_t)(d = dp[0]);
+                if (need_swap) u = swap16(u);
+                *((uint16_t *)words) = u;
+                return ((1 < de - dp || CLEAR_LOWBITS(d, 16) != 0) ? 2 : 1) * sign;
+            }
+#endif
+#if defined(HAVE_UINT32_T) && 4 <= SIZEOF_BDIGITS
+            if (wordsize == 4 && (uintptr_t)words % ALIGNOF(uint32_t) == 0) {
+                uint32_t u = (uint32_t)(d = dp[0]);
+                if (need_swap) u = swap32(u);
+                *((uint32_t *)words) = u;
+                return ((1 < de - dp || CLEAR_LOWBITS(d, 32) != 0) ? 2 : 1) * sign;
+            }
+#endif
+#if defined(HAVE_UINT64_T) && 8 <= SIZEOF_BDIGITS
+            if (wordsize == 8 && (uintptr_t)words % ALIGNOF(uint64_t) == 0) {
+                uint64_t u = (uint64_t)(d = dp[0]);
+                if (need_swap) u = swap64(u);
+                *((uint64_t *)words) = u;
+                return ((1 < de - dp || CLEAR_LOWBITS(d, 64) != 0) ? 2 : 1) * sign;
+            }
+#endif
+        }
+        else { /* sign < 0 && (flags & INTEGER_PACK_2COMP) */
+            BDIGIT_DBL_SIGNED d;
+            if (wordsize == 1) {
+                *((unsigned char *)words) = (unsigned char)(d = -(BDIGIT_DBL_SIGNED)dp[0]);
+                return (1 < de - dp || FILL_LOWBITS(d, 8) != -1) ? -2 : -1;
+            }
+#if defined(HAVE_UINT16_T) && 2 <= SIZEOF_BDIGITS
+            if (wordsize == 2 && (uintptr_t)words % ALIGNOF(uint16_t) == 0) {
+                uint16_t u = (uint16_t)(d = -(BDIGIT_DBL_SIGNED)dp[0]);
+                if (need_swap) u = swap16(u);
+                *((uint16_t *)words) = u;
+                return (wordsize == SIZEOF_BDIGITS && de - dp == 2 && dp[1] == 1 && dp[0] == 0) ? -1 :
+                    (1 < de - dp || FILL_LOWBITS(d, 16) != -1) ? -2 : -1;
+            }
+#endif
+#if defined(HAVE_UINT32_T) && 4 <= SIZEOF_BDIGITS
+            if (wordsize == 4 && (uintptr_t)words % ALIGNOF(uint32_t) == 0) {
+                uint32_t u = (uint32_t)(d = -(BDIGIT_DBL_SIGNED)dp[0]);
+                if (need_swap) u = swap32(u);
+                *((uint32_t *)words) = u;
+                return (wordsize == SIZEOF_BDIGITS && de - dp == 2 && dp[1] == 1 && dp[0] == 0) ? -1 :
+                    (1 < de - dp || FILL_LOWBITS(d, 32) != -1) ? -2 : -1;
+            }
+#endif
+#if defined(HAVE_UINT64_T) && 8 <= SIZEOF_BDIGITS
+            if (wordsize == 8 && (uintptr_t)words % ALIGNOF(uint64_t) == 0) {
+                uint64_t u = (uint64_t)(d = -(BDIGIT_DBL_SIGNED)dp[0]);
+                if (need_swap) u = swap64(u);
+                *((uint64_t *)words) = u;
+                return (wordsize == SIZEOF_BDIGITS && de - dp == 2 && dp[1] == 1 && dp[0] == 0) ? -1 :
+                    (1 < de - dp || FILL_LOWBITS(d, 64) != -1) ? -2 : -1;
+            }
+#endif
+        }
+    }
+#if !defined(WORDS_BIGENDIAN)
+    if (nails == 0 && SIZEOF_BDIGITS == sizeof(BDIGIT) &&
+        (flags & INTEGER_PACK_WORDORDER_MASK) == INTEGER_PACK_LSWORD_FIRST &&
+        (flags & INTEGER_PACK_BYTEORDER_MASK) != INTEGER_PACK_MSBYTE_FIRST) {
+        size_t src_size = num_bdigits * SIZEOF_BDIGITS;
+        size_t dst_size = numwords * wordsize;
+        int overflow = 0;
+        while (0 < src_size && ((unsigned char *)ds)[src_size-1] == 0)
+            src_size--;
+        if (src_size <= dst_size) {
+            MEMCPY(words, dp, char, src_size);
+            MEMZERO((char*)words + src_size, char, dst_size - src_size);
+        }
+        else {
+            MEMCPY(words, dp, char, dst_size);
+            overflow = 1;
+        }
+        if (sign < 0 && (flags & INTEGER_PACK_2COMP)) {
+            unsigned char *p = words, *e = (unsigned char *)words + dst_size;
+            while (p < e && *p == 0)
+                p++;
+            if (p < e) {
+                *p = 1 + (unsigned char)~*p;
+                p++;
+                while (p < e) {
+                    *p = (unsigned char)~*p;
+                    p++;
+                }
+            }
+            else if (overflow) {
+                p = (unsigned char *)dp + dst_size;
+                e = (unsigned char *)dp + src_size;
+                if (p < e && *p++ == 1) {
+                    while (p < e && *p == 0)
+                        p++;
+                    if (p == e)
+                        overflow = 0;
+                }
+            }
+        }
+        if (overflow)
+            sign *= 2;
+        return sign;
+    }
+#endif
+    if (nails == 0 && SIZEOF_BDIGITS == sizeof(BDIGIT) &&
+        wordsize % SIZEOF_BDIGITS == 0 && (uintptr_t)words % ALIGNOF(BDIGIT) == 0) {
+        size_t buf_num_bdigits = numwords * wordsize / SIZEOF_BDIGITS;
+        int need_swap =
+            (flags & INTEGER_PACK_BYTEORDER_MASK) != INTEGER_PACK_NATIVE_BYTE_ORDER &&
+            ((flags & INTEGER_PACK_MSBYTE_FIRST) ? !HOST_BIGENDIAN_P : HOST_BIGENDIAN_P);
+        size_t i;
+        int overflow = 0;
+        if (num_bdigits <= buf_num_bdigits) {
+            MEMCPY(words, dp, BDIGIT, num_bdigits);
+            MEMZERO((BDIGIT*)words + num_bdigits, BDIGIT, buf_num_bdigits - num_bdigits);
+        }
+        else {
+            MEMCPY(words, dp, BDIGIT, buf_num_bdigits);
+            overflow = 1;
+        }
+        if (sign < 0 && (flags & INTEGER_PACK_2COMP)) {
+            int zero_p = bary_2comp(words, buf_num_bdigits);
+            if (overflow &&
+                buf_num_bdigits == num_bdigits-1 &&
+                dp[buf_num_bdigits] == 1 &&
+                zero_p)
+                overflow = 0;
+        }
+        if (need_swap) {
+            for (i = 0; i < buf_num_bdigits; i++) {
+                BDIGIT d = ((BDIGIT*)words)[i];
+                ((BDIGIT*)words)[i] = swap_bdigit(d);
+            }
+        }
+        if (flags & INTEGER_PACK_MSWORD_FIRST) {
+            BDIGIT *p1 = words, *p2 = p1 + buf_num_bdigits - 1;
+            while (p1 < p2) {
+                BDIGIT tmp = *p1;
+                *p1 = *p2;
+                *p2 = tmp;
+                p1++;
+                p2--;
+            }
+        }
+        if (overflow)
+            sign *= 2;
+        return sign;
+    }
+
     buf = words;
     bufend = buf + numwords * wordsize;
 

internal.h

@@ -73,6 +73,43 @@ extern "C" {
     (INTEGER_PACK_MSWORD_FIRST | \
      INTEGER_PACK_MSBYTE_FIRST)
 
+#ifndef swap16
+# define swap16(x)      ((uint16_t)((((x)&0xFF)<<8) | (((x)>>8)&0xFF)))
+#endif
+
+#ifndef swap32
+# if GCC_VERSION_SINCE(4,3,0)
+#  define swap32(x) __builtin_bswap32(x)
+# endif
+#endif
+
+#ifndef swap32
+# define swap32(x)      ((uint32_t)((((x)&0xFF)<<24)    \
+                        |(((x)>>24)&0xFF)       \
+                        |(((x)&0x0000FF00)<<8)  \
+                        |(((x)&0x00FF0000)>>8)  ))
+#endif
+
+#ifndef swap64
+# if GCC_VERSION_SINCE(4,3,0)
+#  define swap64(x) __builtin_bswap64(x)
+# endif
+#endif
+
+#ifndef swap64
+# ifdef HAVE_INT64_T
+#  define byte_in_64bit(n) ((uint64_t)0xff << (n))
+#  define swap64(x)       ((uint64_t)((((x)&byte_in_64bit(0))<<56)      \
+                           |(((x)>>56)&0xFF)                    \
+                           |(((x)&byte_in_64bit(8))<<40)        \
+                           |(((x)&byte_in_64bit(48))>>40)       \
+                           |(((x)&byte_in_64bit(16))<<24)       \
+                           |(((x)&byte_in_64bit(40))>>24)       \
+                           |(((x)&byte_in_64bit(24))<<8)        \
+                           |(((x)&byte_in_64bit(32))>>8)))
+# endif
+#endif
+
 struct rb_deprecated_classext_struct {
     char conflict[sizeof(VALUE) * 3];
 };

pack.c

@@ -100,43 +100,6 @@ TOKEN_PASTE(swap,x)(xtype z)		\
     return r;				\
 }
 
-#ifndef swap32
-# if GCC_VERSION_SINCE(4,3,0)
-#  define swap32(x) __builtin_bswap32(x)
-# endif
-#endif
-
-#ifndef swap64
-# if GCC_VERSION_SINCE(4,3,0)
-#  define swap64(x) __builtin_bswap64(x)
-# endif
-#endif
-
-#ifndef swap16
-# define swap16(x)	((uint16_t)((((x)&0xFF)<<8) | (((x)>>8)&0xFF)))
-#endif
-
-#ifndef swap32
-# define swap32(x)	((uint32_t)((((x)&0xFF)<<24)	\
-			|(((x)>>24)&0xFF)	\
-			|(((x)&0x0000FF00)<<8)	\
-			|(((x)&0x00FF0000)>>8)	))
-#endif
-
-#ifndef swap64
-# ifdef HAVE_INT64_T
-#  define byte_in_64bit(n) ((uint64_t)0xff << (n))
-#  define swap64(x)       ((uint64_t)((((x)&byte_in_64bit(0))<<56) 	\
-			   |(((x)>>56)&0xFF)	                \
-			   |(((x)&byte_in_64bit(8))<<40)	\
-			   |(((x)&byte_in_64bit(48))>>40)	\
-			   |(((x)&byte_in_64bit(16))<<24)	\
-			   |(((x)&byte_in_64bit(40))>>24)	\
-			   |(((x)&byte_in_64bit(24))<<8)	\
-			   |(((x)&byte_in_64bit(32))>>8)))
-# endif
-#endif
-
 #if SIZEOF_SHORT == 2
 # define swaps(x)	swap16(x)
 #elif SIZEOF_SHORT == 4

test/-ext-/bignum/test_pack.rb

@@ -69,6 +69,55 @@ class TestBignum < Test::Unit::TestCase
       assert_equal([1, "\x00\x12\x00\x34\x00\x56\x00\x78"], 0x12345678.test_pack(4, 2, 8, BIG_ENDIAN))
     end
 
+    def test_pack_overflow
+      assert_equal([-2, "\x1"], (-0x11).test_pack(1, 1, 4, BIG_ENDIAN))
+      assert_equal([-2, "\x0"], (-0x10).test_pack(1, 1, 4, BIG_ENDIAN))
+      assert_equal([-1, "\xF"], (-0x0F).test_pack(1, 1, 4, BIG_ENDIAN))
+      assert_equal([+1, "\xF"], (+0x0F).test_pack(1, 1, 4, BIG_ENDIAN))
+      assert_equal([+2, "\x0"], (+0x10).test_pack(1, 1, 4, BIG_ENDIAN))
+      assert_equal([+2, "\x1"], (+0x11).test_pack(1, 1, 4, BIG_ENDIAN))
+
+      assert_equal([-2, "\x01"], (-0x101).test_pack(1, 1, 0, BIG_ENDIAN))
+      assert_equal([-2, "\x00"], (-0x100).test_pack(1, 1, 0, BIG_ENDIAN))
+      assert_equal([-1, "\xFF"], (-0x0FF).test_pack(1, 1, 0, BIG_ENDIAN))
+      assert_equal([+1, "\xFF"], (+0x0FF).test_pack(1, 1, 0, BIG_ENDIAN))
+      assert_equal([+2, "\x00"], (+0x100).test_pack(1, 1, 0, BIG_ENDIAN))
+      assert_equal([+2, "\x01"], (+0x101).test_pack(1, 1, 0, BIG_ENDIAN))
+
+      assert_equal([-2, "\x00\x00\x00\x00\x00\x00\x00\x01"], (-0x10000000000000001).test_pack(2, 4, 0, BIG_ENDIAN))
+      assert_equal([-2, "\x00\x00\x00\x00\x00\x00\x00\x00"], (-0x10000000000000000).test_pack(2, 4, 0, BIG_ENDIAN))
+      assert_equal([-1, "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"], (-0x0FFFFFFFFFFFFFFFF).test_pack(2, 4, 0, BIG_ENDIAN))
+      assert_equal([+1, "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"], (+0x0FFFFFFFFFFFFFFFF).test_pack(2, 4, 0, BIG_ENDIAN))
+      assert_equal([+2, "\x00\x00\x00\x00\x00\x00\x00\x00"], (+0x10000000000000000).test_pack(2, 4, 0, BIG_ENDIAN))
+      assert_equal([+2, "\x00\x00\x00\x00\x00\x00\x00\x01"], (+0x10000000000000001).test_pack(2, 4, 0, BIG_ENDIAN))
+
+      1.upto(16) {|wordsize|
+        1.upto(20) {|numwords|
+          w = numwords*wordsize
+          n = 256**w
+          assert_equal([-2, "\x00"*(w-1)+"\x01"], (-n-1).test_pack(numwords, wordsize, 0, BIG_ENDIAN))
+          assert_equal([-2, "\x00"*w],            (-n  ).test_pack(numwords, wordsize, 0, BIG_ENDIAN))
+          assert_equal([-1, "\xFF"*w],            (-n+1).test_pack(numwords, wordsize, 0, BIG_ENDIAN))
+          assert_equal([+1, "\xFF"*w],            (+n-1).test_pack(numwords, wordsize, 0, BIG_ENDIAN))
+          assert_equal([+2, "\x00"*w],            (+n  ).test_pack(numwords, wordsize, 0, BIG_ENDIAN))
+          assert_equal([+2, "\x00"*(w-1)+"\x01"], (+n+1).test_pack(numwords, wordsize, 0, BIG_ENDIAN))
+        }
+      }
+
+      1.upto(16) {|wordsize|
+        1.upto(20) {|numwords|
+          w = numwords*wordsize
+          n = 256**w
+          assert_equal([-2, "\x01"+"\x00"*(w-1)], (-n-1).test_pack(numwords, wordsize, 0, LITTLE_ENDIAN))
+          assert_equal([-2, "\x00"*w],            (-n  ).test_pack(numwords, wordsize, 0, LITTLE_ENDIAN))
+          assert_equal([-1, "\xFF"*w],            (-n+1).test_pack(numwords, wordsize, 0, LITTLE_ENDIAN))
+          assert_equal([+1, "\xFF"*w],            (+n-1).test_pack(numwords, wordsize, 0, LITTLE_ENDIAN))
+          assert_equal([+2, "\x00"*w],            (+n  ).test_pack(numwords, wordsize, 0, LITTLE_ENDIAN))
+          assert_equal([+2, "\x01"+"\x00"*(w-1)], (+n+1).test_pack(numwords, wordsize, 0, LITTLE_ENDIAN))
+        }
+      }
+    end
+
     def test_pack_sign
       assert_equal([-1, "\x01"], (-1).test_pack(1, 1, 0, BIG_ENDIAN))
       assert_equal([-1, "\x80\x70\x60\x50\x40\x30\x20\x10"], (-0x8070605040302010).test_pack(8, 1, 0, BIG_ENDIAN))
@@ -116,6 +165,33 @@ class TestBignum < Test::Unit::TestCase
       assert_equal([+1, "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"], (+0x0FFFFFFFFFFFFFFFF).test_pack(2, 4, 0, TWOCOMP|BIG_ENDIAN))
       assert_equal([+2, "\x00\x00\x00\x00\x00\x00\x00\x00"], (+0x10000000000000000).test_pack(2, 4, 0, TWOCOMP|BIG_ENDIAN))
       assert_equal([+2, "\x00\x00\x00\x00\x00\x00\x00\x01"], (+0x10000000000000001).test_pack(2, 4, 0, TWOCOMP|BIG_ENDIAN))
+
+      1.upto(16) {|wordsize|
+        1.upto(20) {|numwords|
+          w = numwords*wordsize
+          n = 256**w
+          assert_equal([-2, "\xFF"*w           ], (-n-1).test_pack(numwords, wordsize, 0, TWOCOMP|BIG_ENDIAN))
+          assert_equal([-1, "\x00"*w],            (-n  ).test_pack(numwords, wordsize, 0, TWOCOMP|BIG_ENDIAN))
+          assert_equal([-1, "\x00"*(w-1)+"\x01"], (-n+1).test_pack(numwords, wordsize, 0, TWOCOMP|BIG_ENDIAN))
+          assert_equal([+1, "\xFF"*w],            (+n-1).test_pack(numwords, wordsize, 0, TWOCOMP|BIG_ENDIAN))
+          assert_equal([+2, "\x00"*w],            (+n  ).test_pack(numwords, wordsize, 0, TWOCOMP|BIG_ENDIAN))
+          assert_equal([+2, "\x00"*(w-1)+"\x01"], (+n+1).test_pack(numwords, wordsize, 0, TWOCOMP|BIG_ENDIAN))
+        }
+      }
+
+      1.upto(16) {|wordsize|
+        1.upto(20) {|numwords|
+          w = numwords*wordsize
+          n = 256**w
+          assert_equal([-2, "\xFF"*w           ], (-n-1).test_pack(numwords, wordsize, 0, TWOCOMP|LITTLE_ENDIAN))
+          assert_equal([-1, "\x00"*w],            (-n  ).test_pack(numwords, wordsize, 0, TWOCOMP|LITTLE_ENDIAN))
+          assert_equal([-1, "\x01"+"\x00"*(w-1)], (-n+1).test_pack(numwords, wordsize, 0, TWOCOMP|LITTLE_ENDIAN))
+          assert_equal([+1, "\xFF"*w],            (+n-1).test_pack(numwords, wordsize, 0, TWOCOMP|LITTLE_ENDIAN))
+          assert_equal([+2, "\x00"*w],            (+n  ).test_pack(numwords, wordsize, 0, TWOCOMP|LITTLE_ENDIAN))
+          assert_equal([+2, "\x01"+"\x00"*(w-1)], (+n+1).test_pack(numwords, wordsize, 0, TWOCOMP|LITTLE_ENDIAN))
+        }
+      }
+
     end
 
     def test_unpack_zero