Better list_to_integer

Now tries to use whole width of signed long (Sint) and this halves amount of
multiplications needed to parse long integers. New code is 2-3 times faster
than the old code for large inputs (tens and hundreds of digits), behavior
should not change for small inputs.

Test ran 10k times with GC forced between attempts.

Was (R17):
720 el base 10: 0.14682 sec; base 16: 0.192722 sec; base 36: 0.337118 sec.
2800 el base 10: 1.794133 sec; base 16: 2.735106 sec; base 36: 4.761108 sec.
6500 el base 10: 9.316434 sec; base 16: 14.109469 sec; base 36: 25.319263 sec.

Now (R19 Dev)
720 el base 10: 0.10265 sec; base 16: 0.10851 sec; base 36: 0.160478 sec.
2800 el base 10: 1.002793 sec; base 16: 1.360649 sec; base 36: 2.174309 sec.
6500 el base 10: 4.722197 sec; base 16: 6.60522 sec; base 36: 10.552795 sec.

Added test for corner cases and sign bit corruption. Replaced macros with
inline and hid it inside C file to not pollute global namespace

Old bug in #define LG2_LOOKUP: Replaced with inline function and table
recalculated for all bases 2 to 36 (was 2 to 64)

1 files changed, 17 insertions, 31 deletions

diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index d519216fbd..34611ad6ab 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -2904,8 +2904,11 @@ BIF_RETTYPE integer_to_list_1(BIF_ALIST_1)
 
 /**********************************************************************/
 
-/* convert a list of ascii ascii integer value to an integer */
-
+/*
+ * Converts a list of ascii base10 digits to an integer fully or partially.
+ * Returns result and the remaining tail.
+ * On error returns: {error,not_a_list}, or {error, no_integer}
+ */
 
 BIF_RETTYPE string_to_integer_1(BIF_ALIST_1)
 {
@@ -2913,9 +2916,8 @@ BIF_RETTYPE string_to_integer_1(BIF_ALIST_1)
      Eterm tail;
      Eterm *hp;
      /* must be a list */
-     switch (do_list_to_integer(BIF_P,BIF_ARG_1,&res,&tail)) {
-	 /* HAlloc after do_list_to_integer as it 
-	    might HAlloc itself (bignum) */
+     switch (erts_list_to_integer(BIF_P, BIF_ARG_1, 10, &res, &tail)) {
+     /* HAlloc after erts_list_to_integer as it might HAlloc itself (bignum) */
      case LTI_BAD_STRUCTURE:
 	 hp = HAlloc(BIF_P,3);
 	 BIF_RET(TUPLE2(hp, am_error, am_not_a_list));
@@ -2930,13 +2932,14 @@ BIF_RETTYPE string_to_integer_1(BIF_ALIST_1)
 
 BIF_RETTYPE list_to_integer_1(BIF_ALIST_1)
  {
-   /* Using do_list_to_integer is about twice as fast as using 
+   /* Using erts_list_to_integer is about twice as fast as using
       erts_chars_to_integer because we do not have to copy the 
       entire list */
      Eterm res;
      Eterm dummy;
      /* must be a list */
-     if (do_list_to_integer(BIF_P,BIF_ARG_1,&res,&dummy) != LTI_ALL_INTEGER) {
+     if (erts_list_to_integer(BIF_P, BIF_ARG_1, 10,
+                              &res, &dummy) != LTI_ALL_INTEGER) {
 	 BIF_ERROR(BIF_P,BADARG);
      }
      BIF_RET(res);
@@ -2944,14 +2947,12 @@ BIF_RETTYPE list_to_integer_1(BIF_ALIST_1)
 
 BIF_RETTYPE list_to_integer_2(BIF_ALIST_2)
 {
-
   /* Bif implementation is about 50% faster than pure erlang,
      and since we have erts_chars_to_integer now it is simpler
      as well. This could be optmized further if we did not have to
      copy the list to buf. */
     int i;
-    Eterm res;
-    char *buf = NULL;
+    Eterm res, dummy;
     int base;
 
     i = erts_list_length(BIF_ARG_1);
@@ -2959,31 +2960,16 @@ BIF_RETTYPE list_to_integer_2(BIF_ALIST_2)
       BIF_ERROR(BIF_P, BADARG);
     
     base = signed_val(BIF_ARG_2);
-  
+
     if (base < 2 || base > 36) 
       BIF_ERROR(BIF_P, BADARG);
 
-    /* Take fast path if base it 10 */
-    if (base == 10)
-      return list_to_integer_1(BIF_P,&BIF_ARG_1);
-    
-    buf = (char *) erts_alloc(ERTS_ALC_T_TMP, i + 1);
-    
-    if (intlist_to_buf(BIF_ARG_1, buf, i) < 0)
-      goto list_to_integer_1_error;
-    buf[i] = '\0';		/* null terminal */
-    
-    if ((res = erts_chars_to_integer(BIF_P,buf,i,base)) == THE_NON_VALUE)
-      goto list_to_integer_1_error;
-    
-    erts_free(ERTS_ALC_T_TMP, (void *) buf);
+    if (erts_list_to_integer(BIF_P, BIF_ARG_1, base,
+                             &res, &dummy) != LTI_ALL_INTEGER) {
+        BIF_ERROR(BIF_P,BADARG);
+    }
     BIF_RET(res);
-    
- list_to_integer_1_error:
-    erts_free(ERTS_ALC_T_TMP, (void *) buf);
-    BIF_ERROR(BIF_P, BADARG);
-     
- }
+}
 
 /**********************************************************************/