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3-334 Vol. 2A FIST/FISTP—Store Integer
INSTRUCTION SET REFERENCE, A-M
FIST/FISTP—Store Integer
Description
The FIST instruction converts the value in the ST(0) register to a signed integer and
stores the result in the destination operand. Values can be stored in word or double-
word integer format. The destination operand specifies the address where the first
byte of the destination value is to be stored.
The FISTP instruction performs the same operation as the FIST instruction and then
pops the register stack. To pop the register stack, the processor marks the ST(0)
register as empty and increments the stack pointer (TOP) by 1. The FISTP instruction
also stores values in quadword integer format.
The following table shows the results obtained when storing various classes of
numbers in integer format.
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
DF /2 FIST m16int Valid Valid Store ST(0) in m16int.
DB /2 FIST m32int Valid Valid Store ST(0) in m32int.
DF /3 FISTP m16int Valid Valid Store ST(0) in m16int and pop
register stack.
DB /3 FISTP m32int Valid Valid Store ST(0) in m32int and pop
register stack.
DF /7 FISTP m64int Valid Valid Store ST(0) in m64int and pop
register stack.
Table 3-32. FIST/FISTP Results
ST(0) DEST
−∞ or Value Too Large for DEST Format *
F ≤ −1
- I
−
1 < F < −0 **
−00
+00
+0 < F < +1**
F ≥ +1+ I
+
∞ or Value Too Large for DEST Format *