[llvm-commits] [llvm] r64332 - /llvm/trunk/docs/LangRef.html

[Dale Johannesen]

Author: johannes
Date: Wed Feb 11 16:14:51 2009
New Revision: 64332

URL: http://llvm.org/viewvc/llvm-project?rev=64332&view=rev
Log:
Edit description of floating point constants to
reflect reality.  Acknowledgements to John Clements
for prodding me into this.


Modified:
    llvm/trunk/docs/LangRef.html

Modified: llvm/trunk/docs/LangRef.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.html?rev=64332&r1=64331&r2=64332&view=diff

==============================================================================
--- llvm/trunk/docs/LangRef.html (original)
+++ llvm/trunk/docs/LangRef.html Wed Feb 11 16:14:51 2009
@@ -1760,16 +1760,31 @@
 
 </dl>
 
-<p>The one non-intuitive notation for constants is the optional hexadecimal form
+<p>The one non-intuitive notation for constants is the hexadecimal form
 of floating point constants.  For example, the form '<tt>double
 0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
 4.5e+15</tt>'.  The only time hexadecimal floating point constants are required
 (and the only time that they are generated by the disassembler) is when a 
 floating point constant must be emitted but it cannot be represented as a 
-decimal floating point number.  For example, NaN's, infinities, and other 
+decimal floating point number in a reasonable number of digits.  For example,
+NaN's, infinities, and other 
 special values are represented in their IEEE hexadecimal format so that 
 assembly and disassembly do not cause any bits to change in the constants.</p>
-
+<p>When using the hexadecimal form, constants of types float and double are
+represented using the 16-digit form shown above (which matches the IEEE754
+representation for double); float values must, however, be exactly representable
+as IEE754 single precision.
+Hexadecimal format is always used for long
+double, and there are three forms of long double.  The 80-bit
+format used by x86 is represented as <tt>0xK</tt>
+followed by 20 hexadecimal digits.
+The 128-bit format used by PowerPC (two adjacent doubles) is represented
+by <tt>0xM</tt> followed by 32 hexadecimal digits.  The IEEE 128-bit
+format is represented
+by <tt>0xL</tt> followed by 32 hexadecimal digits; no currently supported
+target uses this format.  Long doubles will only work if they match
+the long double format on your target.  All hexadecimal formats are big-endian
+(sign bit at the left).</p>
 </div>
 
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