Changes between Version 18 and Version 19 of ReplacingGMPNotes/TheCurrentGMPImplementation

Timestamp:

Jan 17, 2007 2:25:33 AM (13 years ago)

Author:

p_tanski

Comment:

add clarification

ReplacingGMPNotes/TheCurrentGMPImplementation

@@ -109 +109 @@
 === GMP Library Implementation ===
 
-[general notes, not finished] The GMP library, like most multi-precision libraries has a fundamental limitation that might seem odd if you are only familiar with Haskell--not likely, but it bears mention anyway!  GMP functions require that their operands be separate entities.  (Remember: an operation such as `a + b` has three entities: the two operands and the result.)  That is, if you want to add `mpz_t a` to `mpz_t b`, and place the result in `mpz_t c`, you are fine but if you try to add `a` to `a` you will run into trouble.  (The problem is, the multi-precision integer library functions are designed so the operands cannot alias; this is more of a problem for complex operations such as multiplication than simple operations like addition.)  This limitation might be overcome by designing the API differently, for example:
+The GMP library, like most multi-precision libraries has a fundamental limitation that might seem odd if you are only familiar with Haskell--not likely, but it bears mention anyway!  GMP functions require that their operands be separate entities.  (Remember: an operation such as `a + b` has three entities: the two operands and the result.)  That is, if you want to add `mpz_t a` to `mpz_t b`, and place the result in `mpz_t c`, you are fine but if you try to add `a` to `a` you will run into trouble.  (The problem is, the multi-precision integer library functions are designed so the operands cannot alias; this is more of a problem for complex operations such as multiplication than simple operations like addition.)  This limitation might be overcome by designing the API differently, for example:
  1. compare the operands in Haskell, Cmm or whatever before you pass them to the _add function; 
  2. if the operands are the same, create a separate copy of the operand
  3. -- you are o.k. for the case where two operands cannot be the same.  
 
-For the case where one of the operands and the result is the same you would have to check outside the general Haskell, Cmm or whatever function wrapping the _add function--you would seem to need a higher level construct.  This is also a problem with Ints in GHCi.  Here is an example:
+For the case where one of the operands and the result is the same you would have to check outside the general Haskell, Cmm or whatever function wrapping the _add function--you would seem to need a higher level construct.  This is already handled by the Haskell language, since `Integer`s are subject to the same functional properties as other non-mutable variables.  There does seem to be a problem with `Int`s and `Integer`s in GHCi--I (PDT) am not sure whether this is a naming problem (the name after `let` is a binding-name) or an evaluation problem.  Here is an example:
 {{{
 #!html
@@ -127 +127 @@
   <font color=Red>-- a = a + a</font>
   <font color=DarkOrchid>></font> <font color=Blue>let</font> <font color=Black>m_integer</font> <font color=Blue>=</font> <font color=Black>m_integer</font> <font color=Blue>+</font> <font color=Black>m_integer</font>
+  <font color=Red>--"m_integer" after "let" here is a new binding</font>
   <font color=DarkOrchid>></font> <font color=Blue>let</font> <font color=Black>n_integer</font> <font color=Blue>=</font> <font color=Black>m_integer</font> <font color=Blue>+</font> <font color=Black>m_integer</font>