(min_precision): Move from c-decl.c

From-SVN: r8020

gcc/c-common.c

@@ -1346,6 +1346,37 @@ type_for_mode (mode, unsignedp)
   return 0;
 }
 
+/* Return the minimum number of bits needed to represent VALUE in a
+   signed or unsigned type, UNSIGNEDP says which.  */
+
+int
+min_precision (value, unsignedp)
+     tree value;
+     int unsignedp;
+{
+  int log;
+
+  /* If the value is negative, compute its negative minus 1.  The latter
+     adjustment is because the absolute value of the largest negative value
+     is one larger than the largest positive value.  This is equivalent to
+     a bit-wise negation, so use that operation instead.  */
+
+  if (tree_int_cst_sgn (value) < 0)
+    value = fold (build1 (BIT_NOT_EXPR, TREE_TYPE (value), value));
+
+  /* Return the number of bits needed, taking into account the fact
+     that we need one more bit for a signed than unsigned type.  */
+
+  if (integer_zerop (value))
+    log = 0;
+  else if (TREE_INT_CST_HIGH (value) != 0)
+    log = HOST_BITS_PER_WIDE_INT + floor_log2 (TREE_INT_CST_HIGH (value));
+  else
+    log = floor_log2 (TREE_INT_CST_LOW (value));
+
+  return log + 1 + ! unsignedp;
+}
+
 /* Print an error message for invalid operands to arith operation CODE.
    NOP_EXPR is used as a special case (see truthvalue_conversion).  */