Improved memory consumption of String.prototype.concat() with numbers.

Author: VadimZhestikov

src/njs_string.c

@@ -601,56 +601,124 @@ njs_int_t
 njs_string_prototype_concat(njs_vm_t *vm, njs_value_t *args, njs_uint_t nargs,
     njs_index_t unused, njs_value_t *retval)
 {
-    u_char             *p, *start;
-    uint64_t           size, length, mask;
+
+#define NUM_TXT_BUF_LEN  512
+#define MAX_NUM_TXT_LEN  njs_length("-1.7976931348623157e+308")
+
+    char               *n_p, n_txt[NUM_TXT_BUF_LEN];
+    double             num;
+    u_char             *p;
+    uint64_t           sz, size, length;
     njs_int_t          ret;
     njs_uint_t         i;
+    const char         *n_p_max;
     njs_string_prop_t  string;
 
+
+    n_p_max = n_txt + NUM_TXT_BUF_LEN - 2*(sizeof(uint16_t) + MAX_NUM_TXT_LEN);
+    n_p = n_txt;
+
     if (njs_is_null_or_undefined(&args[0])) {
         njs_type_error(vm, "\"this\" argument is null or undefined");
         return NJS_ERROR;
     }
 
-    for (i = 0; i < nargs; i++) {
-        if (!njs_is_string(&args[i])) {
-            ret = njs_value_to_string(vm, &args[i], &args[i]);
-            if (ret != NJS_OK) {
-                return ret;
-            }
-        }
-    }
-
     if (nargs == 1) {
-        njs_string_copy(retval, &args[0]);
+        njs_value_assign(retval, &args[0]);
         return NJS_OK;
     }
 
     size = 0;
     length = 0;
-    mask = -1;
 
     for (i = 0; i < nargs; i++) {
-        (void) njs_string_prop(vm, &string, &args[i]);
+        if (njs_is_number(&args[i])) {
+            num = njs_number(&args[i]);
 
-        size += string.size;
-        length += string.length;
-    }
+            if (isnan(num)) {
+                size += njs_length("NaN");
+                length += njs_length("NaN");
 
-    length &= mask;
+            } else if (isinf(num)) {
+                if (num < 0) {
+                    size += njs_length("-Infinity");
+                    length += njs_length("-Infinity");
 
-    start = njs_string_alloc(vm, retval, size, length);
-    if (njs_slow_path(start == NULL)) {
+                } else {
+                    size += njs_length("Infinity");
+                    length += njs_length("Infinity");
+                }
+
+            } else {
+                sz = njs_dtoa(num,  (char *) n_p + sizeof(uint16_t));
+
+                if (njs_fast_path(n_p < n_p_max)) {
+                    *((uint16_t *)(n_p)) = sz;
+                    n_p += sizeof(uint16_t) + sz;
+                }
+
+                size += sz;
+                length += sz;
+            }
+
+        } else {
+            if (!njs_is_string(&args[i])) {
+                ret = njs_value_to_string(vm, &args[i], &args[i]);
+                if (ret != NJS_OK) {
+                    return ret;
+                }
+
+            }
+
+            njs_string_prop(vm, &string, &args[i]);
+
+            size += string.size;
+            length += string.length;
+        }
+    }
+
+    p = njs_string_alloc(vm, retval, size, length);
+    if (njs_slow_path(p == NULL)) {
         return NJS_ERROR;
     }
 
-    p = start;
+    n_p = n_txt;
 
     for (i = 0; i < nargs; i++) {
-        (void) njs_string_prop(vm, &string, &args[i]);
+        if (njs_is_number(&args[i])) {
+            num = njs_number(&args[i]);
 
-        p = memcpy(p, string.start, string.size);
-        p += string.size;
+            if (isnan(num)) {
+                p = njs_cpymem(p, "NaN", njs_length("NaN"));
+
+            } else if (isinf(num)) {
+                if (num < 0) {
+                    p = njs_cpymem(p, "-Infinity", njs_length("-Infinity"));
+
+                } else {
+                    p = njs_cpymem(p, "Infinity", njs_length("Infinity"));
+                }
+
+            } else {
+                if (njs_fast_path(n_p < n_p_max)) {
+                    length = *((uint16_t *)(n_p));
+
+                    n_p += sizeof(uint16_t);
+                    p = njs_cpymem(p, n_p, length);
+
+                    n_p += length;
+
+                } else {
+                    sz = njs_dtoa(num, (char *) p);
+                    p += sz;
+                }
+            }
+
+        } else {
+            njs_string_prop(vm, &string, &args[i]);
+
+            p = njs_cpymem(p, string.start, string.size);
+        }
     }
 
     return NJS_OK;