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A Very Simple Compiler
A typical assignment for computer science students is to build a compiler that compiles a simple language for a RISC architecture, which, when it goes to extremes, could become: evaluating an expression on an ultimate RISC architecture – a One Instruction Set Computer (OISC).
The target architecture has a memory consisting of 65,536 16-bit words and a 16-bit instruction pointer IP. As suggested by its name, it has only one instruction: subtract-and-branch-if-non-negative. In each instruction cycle, the processor reads three consecutive words a, b and c at the address stored in IP, then subtracts a from the word at address b. If the result is non-negative, IP is set to c, otherwise it is increased by three. (Here by “subtract” and “non-negative” we mean 16-bit signed integer arithmetic.) When IP is greater than or equal to 65,534, the processor halts.
A program is executed as follows:
The source language is an arithmetic expression consisting of only ‘
Given an expression, your task is to compile it into an OISC program.
A quick reference for half-precision floating point
Below are two routines written in C for simplified conversions between half-precision and single-precision floating point numbers.
The input is presented as an expression on a single line. The expression can contain up to 8 arithmetic operators.
The output should be a line of at most 65,536 space-separated integers, each representing a word in the OISC program starting from address 0. Memory unoccupied when the program is loaded will be filled with 0.
0 0 3 -15360 0 65535
Underflow, overflow and special values (zeroes, denormals, infinities and NaNs) will not occur in this problem.
Rounding to single precision before rounding to half precision is always safe in this problem.
POJ Monthly--2007.03.04, Hou, Qiming
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