pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / util / SmallFloat.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/SmallFloat.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/SmallFloat.java
new file mode 100644 (file)
index 0000000..175b533
--- /dev/null
+++ b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/SmallFloat.java
@@ -0,0 +1,124 @@
+package org.apache.lucene.util;
+/**
+ * Copyright 2005 The Apache Software Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+/** Floating point numbers smaller than 32 bits.
+ *
+ * @lucene.internal
+ */
+public class SmallFloat {
+
+  /** Converts a 32 bit float to an 8 bit float.
+   * <br>Values less than zero are all mapped to zero.
+   * <br>Values are truncated (rounded down) to the nearest 8 bit value.
+   * <br>Values between zero and the smallest representable value
+   *  are rounded up.
+   *
+   * @param f the 32 bit float to be converted to an 8 bit float (byte)
+   * @param numMantissaBits the number of mantissa bits to use in the byte, with the remainder to be used in the exponent
+   * @param zeroExp the zero-point in the range of exponent values
+   * @return the 8 bit float representation
+   */
+  public static byte floatToByte(float f, int numMantissaBits, int zeroExp) {
+    // Adjustment from a float zero exponent to our zero exponent,
+    // shifted over to our exponent position.
+    int fzero = (63-zeroExp)<<numMantissaBits;
+    int bits = Float.floatToRawIntBits(f);
+    int smallfloat = bits >> (24-numMantissaBits);
+    if (smallfloat <= fzero) {
+      return (bits<=0) ?
+        (byte)0   // negative numbers and zero both map to 0 byte
+       :(byte)1;  // underflow is mapped to smallest non-zero number.
+    } else if (smallfloat >= fzero + 0x100) {
+      return -1;  // overflow maps to largest number
+    } else {
+      return (byte)(smallfloat - fzero);
+    }
+  }
+
+  /** Converts an 8 bit float to a 32 bit float. */
+  public static float byteToFloat(byte b, int numMantissaBits, int zeroExp) {
+    // on Java1.5 & 1.6 JVMs, prebuilding a decoding array and doing a lookup
+    // is only a little bit faster (anywhere from 0% to 7%)
+    if (b == 0) return 0.0f;
+    int bits = (b&0xff) << (24-numMantissaBits);
+    bits += (63-zeroExp) << 24;
+    return Float.intBitsToFloat(bits);
+  }
+
+
+  //
+  // Some specializations of the generic functions follow.
+  // The generic functions are just as fast with current (1.5)
+  // -server JVMs, but still slower with client JVMs.
+  //
+
+  /** floatToByte(b, mantissaBits=3, zeroExponent=15)
+   * <br>smallest non-zero value = 5.820766E-10
+   * <br>largest value = 7.5161928E9
+   * <br>epsilon = 0.125
+   */
+  public static byte floatToByte315(float f) {
+    int bits = Float.floatToRawIntBits(f);
+    int smallfloat = bits >> (24-3);
+    if (smallfloat <= ((63-15)<<3)) {
+      return (bits<=0) ? (byte)0 : (byte)1;
+    }
+    if (smallfloat >= ((63-15)<<3) + 0x100) {
+      return -1;
+    }
+    return (byte)(smallfloat - ((63-15)<<3));
+ }
+
+  /** byteToFloat(b, mantissaBits=3, zeroExponent=15) */
+  public static float byte315ToFloat(byte b) {
+    // on Java1.5 & 1.6 JVMs, prebuilding a decoding array and doing a lookup
+    // is only a little bit faster (anywhere from 0% to 7%)
+    if (b == 0) return 0.0f;
+    int bits = (b&0xff) << (24-3);
+    bits += (63-15) << 24;
+    return Float.intBitsToFloat(bits);
+  }
+
+
+  /** floatToByte(b, mantissaBits=5, zeroExponent=2)
+   * <br>smallest nonzero value = 0.033203125
+   * <br>largest value = 1984.0
+   * <br>epsilon = 0.03125
+   */
+  public static byte floatToByte52(float f) {
+    int bits = Float.floatToRawIntBits(f);
+    int smallfloat = bits >> (24-5);
+    if (smallfloat <= (63-2)<<5) {
+      return (bits<=0) ? (byte)0 : (byte)1;
+    }
+    if (smallfloat >= ((63-2)<<5) + 0x100) {
+      return -1;
+    }
+    return (byte)(smallfloat - ((63-2)<<5));
+  }
+
+  /** byteToFloat(b, mantissaBits=5, zeroExponent=2) */
+  public static float byte52ToFloat(byte b) {
+    // on Java1.5 & 1.6 JVMs, prebuilding a decoding array and doing a lookup
+    // is only a little bit faster (anywhere from 0% to 7%)
+    if (b == 0) return 0.0f;
+    int bits = (b&0xff) << (24-5);
+    bits += (63-2) << 24;
+    return Float.intBitsToFloat(bits);
+  }
+}