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Added getSaneNumber and getSignedWordValue.

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This commit is contained in:
Robert Greene 2003-02-26 01:29:12 +00:00
parent 08a70ca7ab
commit 71ae6cd4f9
1 changed files with 39 additions and 0 deletions
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39
src/com/webcodepro/applecommander/storage/AppleUtil.java
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@ -62,6 +62,14 @@ public class AppleUtil {
return getUnsignedByte(low) + getUnsignedByte(high)*256; return getUnsignedByte(low) + getUnsignedByte(high)*256;
} }
/**
* Compute the signed value of a word.
*/
public static int getSignedWordValue(byte[] buffer, int offset) {
int value = buffer[offset+1] * 256;
return value + getUnsignedByte(buffer[offset]);
}
/** /**
* Set a word value. * Set a word value.
*/ */
@ -404,4 +412,35 @@ public class AppleUtil {
} }
return decompressedStream.toByteArray(); return decompressedStream.toByteArray();
} }
/**
* Pull a SANE formatted number from the buffer and return it
* as a Java double datatype. Fortunately, SANE is the IEEE 754
* format which _is_ Java's double datatype. The Double class
* has an intrinsic longBitsToDouble method to do this. The
* SANE/IEEE 754 format is setup as such:
* <pre>
* E SSSSSSSSSSS FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF...F<br>
* 0 1........11 12....................................63<br>
* </pre>
* Where E is the sign bit, S is the exponent bits and F is the
* fraction bits. The format is discussed within the Double class
* documentation as around the web. Be aware that the fraction
* bits are base 2. Meaning that a fraction of .101 is, in reality,
* a binary fraction. In decimal, this is 1/2 + 0/4 + 1/8 = 5/8
* or .625.
* See http://www.psc.edu/general/software/packages/ieee/ieee.html
* for an example.
* <p>
* Note: SANE numbers, as stored by AppleWorks are in typical
* low/high format.
*/
public static double getSaneNumber(byte[] buffer, int offset) {
long doubleBits = 0;
for (int i=8; i>0; i--) {
doubleBits <<= 8;
doubleBits+= getUnsignedByte(buffer[offset+i-1]);
}
return Double.longBitsToDouble(doubleBits);
}
} }