FXTRACT splits the value in ST into its exponent and significand. The exponent replaces the original operand on the stack and the significand is pushed onto the stack. Following execution of FXTRACT, ST (the new stack top) contains the value of the original significand expressed as a real number: its sign is the same as the operand's, its exponent is 0 true (16,383 or 3FFFH biased), and its significand is identical to the original operand's. ST(1) contains the value of the original operand's true (unbiased) exponent expressed as a real number.
To illustrate the operation of FXTRACT, assume that ST contains a number whose true exponent is +4 (i.e., its exponent field contains 4003H). After running FXTRACT, ST(1) will contain the real number +4.0; its sign will be positive, its exponent field will contain 4001H (+2 true) and its significand field will contain 1δ00...00B. In other words, the value in ST(1) will be 1.0 * 2² = 4. If ST contains an operand whose true exponent is -7 (i.e., its exponent field contains 3FF8H), then FXTRACT will return an "exponent" of -7.0; after the instruction runs, ST(1)'s sign and exponent fields will contain C001H (negative sign, true exponent of 2), and its significand will be 1δ1100...00B. In other words, the value in ST(1) will be -1.75 * 2²=-7.0. In both cases, following FXTRACT, ST's sign and significand fields will be the same as the original operand's, and its exponent field will contain 3FFFH (0 true).