Simplify arithmetic with a bignum and a small

bjorng · Aug 24, 2023 · 920f26c · 920f26c
1 parent dec8215
commit 920f26c
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Showing 3 changed files with 49 additions and 22 deletions.
diff --git a/erts/emulator/beam/big.c b/erts/emulator/beam/big.c
@@ -2900,12 +2900,22 @@ Eterm big_plus_small(Eterm x, Uint y, Eterm *r)
 				 BIG_V(r)), (short) BIG_SIGN(xp));
 }
 
-Eterm big_times_small(Eterm x, Uint y, Eterm *r)
+Eterm big_mul_small(Eterm x, Eterm y, Eterm *r)
 {
     Eterm* xp = big_val(x);
+    Sint val;
+    short sgn = BIG_SIGN(xp);
 
-    return big_norm(r, D_mul(BIG_V(xp),BIG_SIZE(xp), (ErtsDigit) y, 
-			     BIG_V(r)), (short) BIG_SIGN(xp));
+    ASSERT(is_small(y));
+    val = signed_val(y);
+    if (val < 0) {
+        val = -val;
+        sgn = !sgn;
+    }
+
+    return big_norm(r, D_mul(BIG_V(xp), BIG_SIZE(xp),
+                             (ErtsDigit) val, BIG_V(r)),
+                    sgn);
 }
 
 /*

diff --git a/erts/emulator/beam/big.h b/erts/emulator/beam/big.h
@@ -144,7 +144,7 @@ Eterm big_div(Eterm, Eterm, Eterm*);
 Eterm big_rem(Eterm, Eterm, Eterm*);
 
 Eterm big_plus_small(Eterm, Uint, Eterm*);
-Eterm big_times_small(Eterm, Uint, Eterm*);
+Eterm big_mul_small(Eterm, Eterm, Eterm*);
 
 Eterm big_band(Eterm, Eterm, Eterm*);
 Eterm big_bor(Eterm, Eterm, Eterm*);

diff --git a/erts/emulator/beam/erl_arith.c b/erts/emulator/beam/erl_arith.c
@@ -672,8 +672,6 @@ erts_mixed_minus(Process* p, Eterm arg1, Eterm arg2)
 Eterm
 erts_mixed_times(Process* p, Eterm arg1, Eterm arg2)
 {
-    DECLARE_TMP(tmp_big1,0,p);
-    DECLARE_TMP(tmp_big2,1,p);
     Eterm hdr;
     Eterm res;
     FloatDef f1, f2;
@@ -746,9 +744,23 @@ erts_mixed_times(Process* p, Eterm arg1, Eterm arg2)
 			return(SMALL_ZERO);
 		    if (arg1 == SMALL_ONE)
 			return(arg2);
-		    arg1 = small_to_big(signed_val(arg1), tmp_big1);
-		    sz = 2 + big_size(arg2);
-		    goto do_big;
+                    sz = big_size(arg2) + 1;
+                    need_heap = BIG_NEED_SIZE(sz);
+#ifdef DEBUG
+                    need_heap++;
+#endif
+                    hp = HeapFragOnlyAlloc(p, need_heap);
+#ifdef DEBUG
+                    hp[need_heap-1] = ERTS_HOLE_MARKER;
+#endif
+                    res = big_mul_small(arg2, arg1, hp);
+                    ASSERT(hp[need_heap-1] == ERTS_HOLE_MARKER);
+                    maybe_shrink(p, hp, res, need_heap);
+                    if (is_nil(res)) {
+                        p->freason = SYSTEM_LIMIT;
+                        return THE_NON_VALUE;
+                    }
+		    return res;
 		case (_TAG_HEADER_FLOAT >> _TAG_PRIMARY_SIZE):
 		    f1.fd = signed_val(arg1);
 		    GET_DOUBLE(arg2, f2);
@@ -773,9 +785,24 @@ erts_mixed_times(Process* p, Eterm arg1, Eterm arg2)
 			return(SMALL_ZERO);
 		    if (arg2 == SMALL_ONE)
 			return(arg1);
-		    arg2 = small_to_big(signed_val(arg2), tmp_big2);
-		    sz = 2 + big_size(arg1);
-		    goto do_big;
+                    sz = big_size(arg1) + 1;
+                    need_heap = BIG_NEED_SIZE(sz);
+#ifdef DEBUG
+                    need_heap++;
+#endif
+                    hp = HeapFragOnlyAlloc(p, need_heap);
+
+#ifdef DEBUG
+                    hp[need_heap-1] = ERTS_HOLE_MARKER;
+#endif
+                    res = big_mul_small(arg1, arg2, hp);
+                    ASSERT(hp[need_heap-1] == ERTS_HOLE_MARKER);
+                    maybe_shrink(p, hp, res, need_heap);
+                    if (is_nil(res)) {
+                        p->freason = SYSTEM_LIMIT;
+                        return THE_NON_VALUE;
+                    }
+		    return res;
 		default:
 		    goto badarith;
 		}
@@ -787,26 +814,16 @@ erts_mixed_times(Process* p, Eterm arg1, Eterm arg2)
 		    sz1 = big_size(arg1);
 		    sz2 = big_size(arg2);
 		    sz = sz1 + sz2;
-
-		do_big:
 		    need_heap = BIG_NEED_SIZE(sz);
 #ifdef DEBUG
                     need_heap++;
 #endif
                     hp = HeapFragOnlyAlloc(p, need_heap);
-
 #ifdef DEBUG
                     hp[need_heap-1] = ERTS_HOLE_MARKER;
 #endif
 		    res = big_times(arg1, arg2, hp);
                     ASSERT(hp[need_heap-1] == ERTS_HOLE_MARKER);
-
-		    /*
-		     * Note that the result must be big in this case, since
-		     * at least one operand was big to begin with, and
-		     * the absolute value of the other is > 1.
-		     */
-
                     maybe_shrink(p, hp, res, need_heap);
 		    if (is_nil(res)) {
 			p->freason = SYSTEM_LIMIT;