1. xerox 560 computer system - The UK Mirror Service

Instruction NameFloating Subtract LongFloating Multiply ShortFloating Multiply LongMnemonicFSLFMSFMLfor addition and subtraction, an abnormal zero istreated the same as any nonzero operand.3. A positive floating-point number is normalized if andonly if the fraction is contained in the interval1/16 $ F < 1Floating Divide ShortFloating Divide LongFLOATING-POINT NUMBERSFDSFDLTwo number formats are accommodated for floating-pointarithmetic: short and long. A short-format floating-pointnumber consists of a sign (bit 0), a biased t , base 16 exponent,which is called a characteristic (bits 1-7), and asix-digit hexadecimal fraction (bits 8-31). A long-formatfloating-point number consists of a short-format floatingpointnumber followed by an additional eight hexadecimaldigits of fractional significance, and occupies a doublewordmemory location or an even-odd pair of generalregisters.A floating-point number (N) has the following format:4. A negative floating-point number is the two1s complementof its positive representation.5. A negative floating-point number is normalized if andonly if its two1s complement is a normalized positivenumber.By this definition, a floating-point number of the form1 xxx xxxx 1111 0000 . .• 0000is normalized, and a floating-point number of the form1 xxx xxxx 0000 0000 . .. 0000is illegal and, whenever generated by floating-point instructions,is converted to the form1 yyy yyyy 1111 0000 . .. 0000where yy ... Y is 1 less than xx ... x.examples of floating-point numbers.Table 7 containsModes of OperationA floating-point number (N) has the following formaldefinition:1.C-64N = F x 16where F = 0 or-616 s IFI s 1 (short format) or-1416 S IFI $ 1 {long format)There are four mode control bits that are used to qual ify£"1 __ . .L- __ .• .L ____ .I..- _ _ TI _ _ ___ I. __ L.. I I -.1.__ _IIUUIIII~-PUIIII Upt::IUIIUII:>. 1111::::>1::: IIIUUI::: ,",UIIIIUI Uti:> utI:::identified as FR (floating round), FS (floating significance),FZ (floating zero), and FN (floating normalize); they arecontained in bit positions 4, 5, 6, and 7, respectively, ofthe program status words (PSWs4_7).The floating-point mode is established by setting the fourfloating-point mode control bits. This can be performed byany of the following instructions:Instruction NameMnemonicand 0 $ C $ 127.Load Conditions and Floating ControlLCF2. A positive floating-point number with a fraction ofzero and a characteristic of zero is a "true" zero.A positive floating-point number with a fraction ofzero and a nonzero characteristic is an "abnorma I"zero. For floating-point multiplication and division,an abnormal zero is treated as a true zero. However,Load Conditions and Floating ControlImmediateLoad Program Status WordsExchange Program Status WordsLCFILPSDXPSDThe floating-point mode control bits are stored by executingeither of the following instructions:t The bias value of 4016 is added to the exponent for thepurpose of making it possible to compare the absolute magnitudeof two numbers, i. e., without reference to a signbit. This manipulation effectively removes the sign bit,making each characteristic a 7-bit positive number.Instruction NameStore Conditions and Floating ControlExchange Program Status WordsMnemonicSTCFXPSDFloating-Point Arithmetic Instructions 75