Computer Hardware User's Guide

Floating-Point Conversion (IEEE Std. 754)
5-20
Example 5–5.IEEE-to-TMS320C3x Conversion (Complete Version) (Continued)
* HANDLE NaN AND INFINITY
TSTB *+AR1(7),R0
RETSNZ ; Return if NaN
LDI R0,R0
LDFGT *+AR1(8),R0 ; If positive, infinity =
; most positive number
LDFN *+AR1(5),R0 ; If negative, infinity =
RETS ; most negative number RETS
* HANDLE 0s AND UNNORMALIZED NUMBERS
UNNORM TSTB *+AR1(6),R0 ; Is the MSB of f equal to 1?
LDFZ *+AR1(3),R0 ; If not, force the number to 0
RETSZ ; and return
XOR *+AR1(6),R0 ; If MSB of f = 1, make it 0
BND NEG1
LSH 1,R0 ; Eliminate sign bit
; & line up mantissa
SUBI *+AR1(2),R0 ; Make e = ±127
PUSH R0
POPF R0 ; Put number in floating point format
RETS
NEG1 POPF R0
NEGF R0,R0 ; If negative, negate R0
RETS
* HANDLE THE REGULAR CASES
*
NORMAL AND3 R0,*AR1,R1 ; Replace fraction with 0
BND NEG ; Test sign
ADDI R0,R1 ; Shift sign and exponent inserting 0
SUBI *+AR1(2),R1 ; Unbias exponent
PUSH R1
POPF R0 ; Load this as a flt. pt. number
RETS
NEG POPF R0 ; Load this as a flt. pt. number
NEGF R0,R0 ; Negate if original sign negative
RETS