interval.sourceforge.net/interval

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a repository of open source, verifiably correct implementations of interval arithmetic and interval constraints, and applications thereof.

Java
- ia_math
  A 100% java, verifiable implementation of interval arithmetic operations and primitive constraint contractions for the arithmetic operators and the elementary functions. including provably correct implementations of the elementary functions (exp,log,sin,cos,tan,asin,acos,atan).
Scheme
- iaeval a simple expression evaluator for intervals,
- giaeval an evaluator for interval expressions with open/closed endpoints,
  An interval arithmetic evaluator written in the JScheme (formerly Silk) dialect of Scheme.
C
- smathlib
  A provably correct implementation of interval arithmetic operations and primitive constraint contractors for the arithmetic operators (real, integer, and boolean), elementary functions (exp,log,sin,cos,tan,asin,acos,atan,sin2pi,...).
Prolog
- clip
  A foreign file extension of GNUProlog in which interval arithmetic constraints are enclosed in curly braces.

RedHat Linux 6.1 on the PC and Macintosh OS X
Note: Porting to other architectures should not be hard. The only non-portable code is that which deals with setting the rounding modes!