buffer: improve copy() performance

PR-URL: https://github.com/nodejs/node/pull/29066
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/buffer.js

@@ -25,7 +25,6 @@ const { Math, Object } = primordials;
 
 const {
   byteLengthUtf8,
-  copy: _copy,
   compare: _compare,
   compareOffset,
   createFromString,
@@ -69,6 +68,7 @@ const {
     ERR_INVALID_ARG_VALUE,
     ERR_INVALID_BUFFER_SIZE,
     ERR_INVALID_OPT_VALUE,
+    ERR_OUT_OF_RANGE,
     ERR_UNKNOWN_ENCODING
   },
   hideStackFrames
@@ -157,6 +157,74 @@ function showFlaggedDeprecation() {
   bufferWarningAlreadyEmitted = true;
 }
 
+function toInteger(n, defaultVal) {
+  n = +n;
+  if (!Number.isNaN(n) &&
+      n >= Number.MIN_SAFE_INTEGER &&
+      n <= Number.MAX_SAFE_INTEGER) {
+    return ((n % 1) === 0 ? n : Math.floor(n));
+  }
+  return defaultVal;
+}
+
+function _copy(source, target, targetStart, sourceStart, sourceEnd) {
+  if (!isUint8Array(source))
+    throw new ERR_INVALID_ARG_TYPE('source', ['Buffer', 'Uint8Array'], source);
+  if (!isUint8Array(target))
+    throw new ERR_INVALID_ARG_TYPE('target', ['Buffer', 'Uint8Array'], target);
+
+  if (targetStart === undefined) {
+    targetStart = 0;
+  } else {
+    targetStart = toInteger(targetStart, 0);
+    if (targetStart < 0)
+      throw new ERR_OUT_OF_RANGE('targetStart', '>= 0', targetStart);
+  }
+
+  if (sourceStart === undefined) {
+    sourceStart = 0;
+  } else {
+    sourceStart = toInteger(sourceStart, 0);
+    if (sourceStart < 0)
+      throw new ERR_OUT_OF_RANGE('sourceStart', '>= 0', sourceStart);
+  }
+
+  if (sourceEnd === undefined) {
+    sourceEnd = source.length;
+  } else {
+    sourceEnd = toInteger(sourceEnd, 0);
+    if (sourceEnd < 0)
+      throw new ERR_OUT_OF_RANGE('sourceEnd', '>= 0', sourceEnd);
+  }
+
+  if (targetStart >= target.length || sourceStart >= sourceEnd)
+    return 0;
+
+  if (sourceStart > source.length) {
+    throw new ERR_OUT_OF_RANGE('sourceStart',
+                               `<= ${source.length}`,
+                               sourceStart);
+  }
+
+  if (sourceEnd - sourceStart > target.length - targetStart)
+    sourceEnd = sourceStart + target.length - targetStart;
+
+  let nb = sourceEnd - sourceStart;
+  const targetLen = target.length - targetStart;
+  const sourceLen = source.length - sourceStart;
+  if (nb > targetLen)
+    nb = targetLen;
+  if (nb > sourceLen)
+    nb = sourceLen;
+
+  if (sourceStart !== 0 || sourceEnd !== source.length)
+    source = new Uint8Array(source.buffer, source.byteOffset + sourceStart, nb);
+
+  target.set(source, targetStart);
+
+  return nb;
+}
+
 /**
  * The Buffer() constructor is deprecated in documentation and should not be
  * used moving forward. Rather, developers should use one of the three new