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3-294 Vol. 2A FBLD—Load Binary Coded Decimal
INSTRUCTION SET REFERENCE, A-M
FBLD—Load Binary Coded Decimal
Description
Converts the BCD source operand into double extended-precision floating-point
format and pushes the value onto the FPU stack. The source operand is loaded
without rounding errors. The sign of the source operand is preserved, including that
of −0.
The packed BCD digits are assumed to be in the range 0 through 9; the instruction
does not check for invalid digits (AH through FH). Attempting to load an invalid
encoding produces an undefined result.
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
Operation
TOP ← TOP − 1;
ST(0) ← ConvertToDoubleExtendedPrecisionFP(SRC);
FPU Flags Affected
C1 Set to 1 if stack overflow occurred; otherwise, set to 0.
C0, C2, C3 Undefined.
Floating-Point Exceptions
#IS Stack overflow occurred.
Protected Mode Exceptions
#GP(0) If a memory operand effective address is outside the CS, DS,
ES, FS, or GS segment limit.
If the DS, ES, FS, or GS register contains a NULL segment
selector.
#SS(0) If a memory operand effective address is outside the SS
segment limit.
#NM CR0.EM[bit 2] or CR0.TS[bit 3] = 1.
#PF(fault-code) If a page fault occurs.
#AC(0) If alignment checking is enabled and an unaligned memory
reference is made while the current privilege level is 3.
#UD If the LOCK prefix is used.
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
DF /4 FBLD m80 dec Valid Valid Convert BCD value to floating-point and
push onto the FPU stack.