Version 4.2.1.8 (now in SVN) starts an experiment with performance-oriented unsafe operations.
The new `scheme/unsafe/ops' library provides operations such as `unsafe-vector-ref' and `unsafe-fl+' (for inexact real addition) that are inlined by the JIT without contract checks. If a call violates the contract of a function from `scheme/unsafe/ops', arbitrarily bad things can happen. As long as contracts are satisfied, however, performance should be a little better than with corresponding safe operations. As part of the experiment, the expansion of `for' with `in-range' and `in-vector' now uses unsafe operations (in a safe way). For example, `in-vector' uses `unsafe-vector-ref' as well as a fixnum comparison for detecting when it has reached the end of a vector; it also uses unsafe fixnum arithmetic to increment the index as long as the step is 1 or -1 (in which case no overflow can occur during the increment). These improvements make a 10-20% difference in a tight loop over a vector. Future possible directions include making the JIT specialize combinations of inexact operations to avoid boxing intermediate results. The exports of `scheme/unsafe/ops' are protected, so that a code inspector can prevent access to unsafe operations by untrusted code. _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
