New long_lshift, without restriction on size of shift count, by Tim Peters.

This makes it possible to write 1L<<1000000, memory permitting.

diff --git a/Objects/longobject.c b/Objects/longobject.c
index 8de545694360dc9f1bbee0f619a3f503dc759dda..123d570b2bf0a057bf5a9f7621d5d0885ab16854 100644 (file)
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -1214,10 +1214,11 @@ long_lshift(a, b)
        longobject *a;
        longobject *b;
 {
+       /* This version due to Tim Peters */
        longobject *z;
        long shiftby;
-       int newsize, wordshift, loshift, hishift, i, j;
-       digit lomask, himask;
+       int oldsize, newsize, wordshift, remshift, i, j;
+       twodigits accum;
        
        shiftby = getlongvalue((object *)b);
        if (shiftby == -1L && err_occurred())
@@ -1226,26 +1227,18 @@ long_lshift(a, b)
                err_setstr(ValueError, "negative shift count");
                return NULL;
        }
-       if (shiftby > MASK) {
+       if ((long)(int)shiftby != shiftby) {
                err_setstr(ValueError, "outrageous left shift count");
                return NULL;
        }
-       if (shiftby % SHIFT == 0) {
-               wordshift = shiftby / SHIFT;
-               loshift = 0;
-               hishift = SHIFT;
-               newsize = ABS(a->ob_size) + wordshift;
-               lomask = MASK;
-               himask = 0;
-       }
-       else {
-               wordshift = shiftby / SHIFT + 1;
-               loshift = SHIFT - shiftby%SHIFT;
-               hishift = shiftby % SHIFT;
-               newsize = ABS(a->ob_size) + wordshift;
-               lomask = ((digit)1 << hishift) - 1;
-               himask = MASK ^ lomask;
-       }
+       /* wordshift, remshift = divmod(shiftby, SHIFT) */
+       wordshift = (int)shiftby / SHIFT;
+       remshift  = (int)shiftby - wordshift * SHIFT;
+
+       oldsize = ABS(a->ob_size);
+       newsize = oldsize + wordshift;
+       if (remshift)
+               ++newsize;
        z = alloclongobject(newsize);
        if (z == NULL)
                return NULL;
@@ -1253,13 +1246,16 @@ long_lshift(a, b)
                z->ob_size = -(z->ob_size);
        for (i = 0; i < wordshift; i++)
                z->ob_digit[i] = 0;
-       for (i = wordshift, j = 0; i < newsize; i++, j++) {
-               if (i > 0)
-                       z->ob_digit[i-1] |=
-                               (a->ob_digit[j] << hishift) & himask;
-               z->ob_digit[i] =
-                       (a->ob_digit[j] >> loshift) & lomask;
-       }
+       accum = 0;      
+       for (i = wordshift, j = 0; j < oldsize; i++, j++) {
+               accum |= a->ob_digit[j] << remshift;
+               z->ob_digit[i] = (digit)(accum & MASK);
+               accum >>= SHIFT;
+       }
+       if (remshift)
+               z->ob_digit[newsize-1] = (digit)accum;
+       else    
+               assert(!accum);
        return (object *) long_normalize(z);
 }