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Fast control for round unit

  • US 5,245,563 A
  • Filed: 09/20/1991
  • Issued: 09/14/1993
  • Est. Priority Date: 09/20/1991
  • Status: Expired due to Fees
First Claim
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1. A device for controlling a rounding off unit in a computer that performs an arithmetic operation on a pair of n-bit operands A, B to produce an n-bit output, operand A having bit components designated, in order from most to least significant, An-1 An-2 . . . Ai . . . Ao, and operand B having bit components Bn-1 Bn-2 . . . Bi . . . Bo, the computer processing an m-bit intermediate result C, where m≦

  • n, by providing carry information from said intermediate result C to the rounding off unit for rounding off an n-bit word to produce said output, the device being characterized by a first array of logic gates for processing ordered bit components Ai, Bi of said operands in two successive time cycles to produce an m-bit conditional sum word, and a second array of logic gates for simultaneously receiving all bits of the conditional sum word and producing a single output bit corresponding to a logical OR of said bits of the conditional sum word, wherein the first array is an array of m identical cells Fj (j=m, m-1, . . .

         1) comprising first and second ranks of logic gates, the first rank of logic gates comprising in each cell Fj an EXCLUSIVE OR gate connected to receive input bits Aj and Bj, and also comprising an OR gate connected to receive input bits Aj-1, Bj-1, and the second rank of logic gates comprising an EXCLUSIVE OR gate in each cell Fj receiving as its inputs outputs of the EXCLUSIVE OR gate and the OR gate of the first rank of said cell Fj and producing an output bit Sj, so that altogether the first array produces an m-bit conditional sum output word S having bit components equal to the output bits Sj (j=m, m-1, . . .

         1), and wherein the second array is a circuit that ORs the m bits Sj to produce a single output bit, the single output bit being provided as a control signal to the rounding off unit to control rounding of the n-bit output word.

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