The methods high, low and toUCS4 can be optimized, as in
6639443: Character.toCodePoint and Character.toSurrogates can be optimized

In the generate methods, the test
uc <= 0xffff
and
uc < Surrogate.UCS4_MIN

are identical, so the latter code can be deleted.

--- /u/martin/ws/dolphin/src/share/classes/sun/nio/cs/Surrogate.java 2007-05-13 03:03:30.484210000 -0700
+++ /u/martin/ws/concurrent/src/share/classes/sun/nio/cs/Surrogate.java 2007-12-09 20:50:41.580695000 -0800
@@ -90,7 +90,7 @@
      */
     public static char high(int uc) {
  assert neededFor(uc);
- return (char)(0xd800 | (((uc - UCS4_MIN) >> 10) & 0x3ff));
+ return (char)((uc >> 10) + (MIN_HIGH - (UCS4_MIN >> 10)));
     }
 
     /**
@@ -98,15 +98,14 @@
      */
     public static char low(int uc) {
  assert neededFor(uc);
- return (char)(0xdc00 | ((uc - UCS4_MIN) & 0x3ff));
+ return (char)((uc & 0x3ff) + MIN_LOW);
     }
 
     /**
      * Converts the given surrogate pair into a 32-bit UCS-4 character.
      */
     public static int toUCS4(char c, char d) {
- assert isHigh(c) && isLow(d);
- return (((c & 0x3ff) << 10) | (d & 0x3ff)) + 0x10000;
+ return Character.toCodePoint(c, d);
     }
 
     /**
@@ -179,14 +178,14 @@
  * object
  */
  public int parse(char c, CharBuffer in) {
- if (Surrogate.isHigh(c)) {
+ if (Character.isHighSurrogate(c)) {
  if (!in.hasRemaining()) {
  error = CoderResult.UNDERFLOW;
  return -1;
  }
  char d = in.get();
- if (Surrogate.isLow(d)) {
- character = toUCS4(c, d);
+ if (Character.isLowSurrogate(d)) {
+ character = Character.toCodePoint(c, d);
  isPair = true;
  error = null;
  return character;
@@ -194,7 +193,7 @@
  error = CoderResult.malformedForLength(1);
  return -1;
  }
- if (Surrogate.isLow(c)) {
+ if (Character.isLowSurrogate(c)) {
  error = CoderResult.malformedForLength(1);
  return -1;
  }
@@ -221,14 +220,14 @@
  */
  public int parse(char c, char[] ia, int ip, int il) {
  assert (ia[ip] == c);
- if (Surrogate.isHigh(c)) {
+ if (Character.isHighSurrogate(c)) {
  if (il - ip < 2) {
  error = CoderResult.UNDERFLOW;
  return -1;
  }
  char d = ia[ip + 1];
- if (Surrogate.isLow(d)) {
- character = toUCS4(c, d);
+ if (Character.isLowSurrogate(d)) {
+ character = Character.toCodePoint(c, d);
  isPair = true;
  error = null;
  return character;
@@ -236,7 +235,7 @@
  error = CoderResult.malformedForLength(1);
  return -1;
  }
- if (Surrogate.isLow(c)) {
+ if (Character.isLowSurrogate(c)) {
  error = CoderResult.malformedForLength(1);
  return -1;
  }
@@ -296,10 +295,6 @@
  error = null;
  return 1;
  }
- if (uc < Surrogate.UCS4_MIN) {
- error = CoderResult.malformedForLength(len);
- return -1;
- }
  if (uc <= Surrogate.UCS4_MAX) {
  if (dst.remaining() < 2) {
  error = CoderResult.OVERFLOW;
@@ -331,7 +326,7 @@
  * error() will return a descriptive result object
  */
  public int generate(int uc, int len, char[] da, int dp, int dl) {
- if (uc <= 0xffff) {
+ if (uc < Surrogate.UCS4_MIN) {
  if (Surrogate.is(uc)) {
  error = CoderResult.malformedForLength(len);
  return -1;
@@ -344,10 +339,6 @@
  error = null;
  return 1;
  }
- if (uc < Surrogate.UCS4_MIN) {
- error = CoderResult.malformedForLength(len);
- return -1;
- }
  if (uc <= Surrogate.UCS4_MAX) {
  if (dl - dp < 2) {
  error = CoderResult.OVERFLOW;