Refactor text util surrogate helpers

src/module.ts

@@ -10,6 +10,13 @@
 
 import { BuiltinNames } from "./builtins";
 import { Target } from "./common";
+import { 
+  isHighSurrogate, 
+  isLowSurrogate, 
+  combineSurrogates, 
+  SURROGATE_HIGH, 
+  SURROGATE_LOW 
+} from "./util";
 import * as binaryen from "./glue/binaryen";
 
 /** A Binaryen-compatible index. */
@@ -3108,8 +3115,8 @@ function stringLengthUTF8(str: string): usize {
     } else if (c1 <= 0x7FF) {
       len += 2;
     } else if (
-      (c1 & 0xFC00) === 0xD800 && i + 1 < k &&
-      (str.charCodeAt(i + 1) & 0xFC00) === 0xDC00
+      isHighSurrogate(c1) && i + 1 < k &&
+      isLowSurrogate(str.charCodeAt(i + 1))
     ) {
       i++;
       len += 4;
@@ -3146,10 +3153,10 @@ function allocString(str: string | null): usize {
         binaryen.__i32_store8(idx++, (0xC0 |  (c1 >>> 6)       ) as u8);
         binaryen.__i32_store8(idx++, (0x80 | ( c1         & 63)) as u8);
       } else if (
-        (c1 & 0xFC00) === 0xD800 && i + 1 < k &&
-        ((c2 = str.charCodeAt(i + 1)) & 0xFC00) === 0xDC00
+        isHighSurrogate(c1) && i + 1 < k &&
+        isLowSurrogate(c2 = str.charCodeAt(i + 1))
       ) {
-        c1 = 0x10000 + ((c1 & 0x3FF) << 10) | (c2 & 0x3FF);
+        c1 = combineSurrogates(c1, c2);
         ++i;
         binaryen.__i32_store8(idx++, (0xF0 |  (c1 >>> 18)      ) as u8);
         binaryen.__i32_store8(idx++, (0x80 | ((c1 >>> 12) & 63)) as u8);
@@ -3209,10 +3216,11 @@ export function readString(ptr: usize): string | null {
       arr.push(cp);
     } else {
       let ch = cp - 0x10000;
-      arr.push(0xD800 | (ch >>> 10));
-      arr.push(0xDC00 | (ch & 0x3FF));
+      arr.push(SURROGATE_HIGH | (ch >>> 10));
+      arr.push(SURROGATE_LOW | (ch & 0x3FF));
     }
   }
+  // TODO: implement and use String.fromCodePoints
   return String.fromCharCodes(arr);
 }
 

src/tokenizer.ts

@@ -29,7 +29,9 @@ import {
   isIdentifierStart,
   isIdentifierPart,
   isDecimal,
-  isOctal
+  isOctal,
+  isHighSurrogate,
+  isLowSurrogate
 } from "./util";
 
 /** Named token types. */
@@ -976,9 +978,9 @@ export class Tokenizer extends DiagnosticEmitter {
             break;
           }
           let start = pos++;
-          if ( // surrogate pair?
-            (c & 0xFC00) == 0xD800 && pos < end &&
-            ((text.charCodeAt(pos)) & 0xFC00) == 0xDC00
+          if (
+            isHighSurrogate(c) && pos < end &&
+            isLowSurrogate(text.charCodeAt(pos))
           ) ++pos;
           this.error(
             DiagnosticCode.Invalid_character,
@@ -1216,7 +1218,7 @@ export class Tokenizer extends DiagnosticEmitter {
       case CharCode.LINEFEED:
       case CharCode.LINESEPARATOR:
       case CharCode.PARAGRAPHSEPARATOR: return "";
-      default: return String.fromCharCode(c);
+      default: return String.fromCodePoint(c);
     }
   }
 
@@ -1677,7 +1679,7 @@ export class Tokenizer extends DiagnosticEmitter {
       return "";
     }
     this.pos = pos;
-    return String.fromCharCode(value);
+    return String.fromCodePoint(value);
   }
 
   checkForIdentifierStartAfterNumericLiteral(): void {
@@ -1739,12 +1741,7 @@ export class Tokenizer extends DiagnosticEmitter {
         ? text.substring(startIfTaggedTemplate, this.pos)
         : "";
     }
-    return value32 < 0x10000
-      ? String.fromCharCode(value32)
-      : String.fromCharCode(
-        ((value32 - 0x10000) >>> 10) | 0xD800,
-        ((value32 - 0x10000) & 1023) | 0xDC00
-      );
+    return String.fromCodePoint(value32);
   }
 }
 

src/util/text.ts

@@ -175,6 +175,50 @@ export function isWhiteSpace(c: i32): bool {
   }
 }
 
+/** First high (lead) surrogate. */
+export const SURROGATE_HIGH = 0xD800;
+
+/** First low (trail) surrogate. */
+export const SURROGATE_LOW = 0xDC00;
+
+/** Tests if a code unit or code point is a surrogate. */
+export function isSurrogate(c: i32): bool {
+  // F800: 11111 0 0000000000 Mask
+  // D800: 11011 X XXXXXXXXXX Any surrogate
+  return (c & 0xF800) == SURROGATE_HIGH;
+}
+
+/** Tests if a surrogate is a high (lead) surrogate. */
+export function isSurrogateHigh(c: i32): bool {
+  // D800-DBFF
+  return c < SURROGATE_LOW;
+}
+
+/** Tests if a surrogate is a low (trail) surrogate. */
+export function isSurrogateLow(c: i32): bool {
+  // DC00-DFFF
+  return c >= SURROGATE_LOW;
+}
+
+/** Tests if a code unit or code point is a high (lead) surrogate. */
+export function isHighSurrogate(c: i32): bool {
+  // FC00: 11111 1 0000000000 Mask
+  // D800: 11011 0 XXXXXXXXXX High/Lead surrogate
+  return (c & 0xFC00) == SURROGATE_HIGH;
+}
+
+/** Tests if a code unit or code point is a low (trail) surrogate. */
+export function isLowSurrogate(c: i32): bool {
+  // FC00: 11111 1 0000000000 Mask
+  // DC00: 11011 1 XXXXXXXXXX Low/Trail surrogate
+  return (c & 0xFC00) == SURROGATE_LOW;
+}
+
+/** Converts a surrogate pair to its respective code point. */
+export function combineSurrogates(hi: i32, lo: i32): i32 {
+  return 0x10000 + ((hi & 0x3FF) << 10) | (lo & 0x3FF);
+}
+
 export function isAlpha(c: i32): bool {
   let c0 = c | 32; // unify uppercases and lowercases a|A - z|Z
   return c0 >= CharCode.a && c0 <= CharCode.z;