[svn:parrot] r35892 - trunk/docs/book

Author: Whiteknight
Date: Thu Jan 22 08:48:04 2009
New Revision: 35892

Modified:
   trunk/docs/book/ch03_pir_basics.pod

Log:
[Book] a few clarifications on the section about PIR register usage.

Modified: trunk/docs/book/ch03_pir_basics.pod
==============================================================================
--- trunk/docs/book/ch03_pir_basics.pod	(original)
+++ trunk/docs/book/ch03_pir_basics.pod	Thu Jan 22 08:48:04 2009
@@ -86,8 +86,8 @@
 
 PIR code has a variety of ways to store values while you work with
 them. Actually, the only place to store values is in a Parrot register,
-but there are multiple ways to work with these registers. Parrot's
-register names always start with a dollar sign, followed by a single
+but there are multiple ways to work with these registers. Register names
+in PIR always start with a dollar sign, followed by a single
 character that shows whether it is an integer (I), numeric (N), string
 (S), or PMC (P) register, and then the number of the register:
 
@@ -96,20 +96,21 @@
 
 You can have as many registers of each type as you need, Parrot will
 automatically allocate new ones for you. The process is transparent, and
-programmers should never have to worry about it.
-
-Parrot registers are allocated in a linear array, and register numbers
-are indices into this array. Having more registers means Parrot must
-allocate more storage space for them, which can decrease memory efficiency
-and register allocation/fetch performance. In general, it's better to
-keep the number of registers small. However, the number of the register
-does not necessarily correspond to the actual storage location where the
-register data is held. A memory allocator unit translates register names
-in the form "$S0" into an actual fixed memory location. This allocator
+programmers should never have to worry about it. It's worth noting that
+the number of the register does not correspond to the actual memory address
+of the register, and using C<$S1000000> doesn't actually allocate one
+million registers. The PIR register allocator will turn the numbers you've
+provided into actual memory addresses during compilation, and will attempt
+to make very efficient use of memory if it is able. This allocator
 can also help to optimize register usage so that existing registers are
-reused instead of allocating new ones in memory. The short version is that
-the programmer should never have to worry about register allocation, and
-should feel free to use as many as she wants. As with any system, it's
+reused instead of allocating new ones in memory.
+
+Parrot registers are allocated in a linear array. Having more registers
+means Parrot must allocate more storage space for them. Too many allocations
+can decrease memory efficiency and register allocation/fetch performance.
+In general, it's better to keep the number of registers used as small as
+possible. The programmer should never have to worry about register allocation,
+and should feel free to use as many as she wants. As with any system, it's
 a good idea to be mindful of the things that might impact performance
 anyway.