FBLD

Load Binary Coded Decimal

Opcodes

Hex Mnemonic Encoding Long Mode Legacy Mode Description
DF /4 FBLD m80 dec None Valid Valid Convert BCD value to floating-point and push onto the FPU stack.

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.

Pseudo Code

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 are undefined.

Exceptions

Floating-Point Exceptions

Exception Description
#IS Stack overflow occurred.

64-Bit Mode Exceptions

Exception Description
#UD If the LOCK prefix is used.
#AC(0) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
#PF(fault-code) If a page fault occurs.
#MF If there is a pending x87 FPU exception.
#NM CR0.EM[bit 2] or CR0.TS[bit 3] = 1.
#GP(0) If the memory address is in a non-canonical form.
#SS(0) If a memory address referencing the SS segment is in a non-canonical form.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

Virtual-8086 Mode Exceptions

Exception Description
#UD If the LOCK prefix is used.
#AC(0) If alignment checking is enabled and an unaligned memory reference is made.
#PF(fault-code) If a page fault occurs.
#NM CR0.EM[bit 2] or CR0.TS[bit 3] = 1.
#SS(0) If a memory operand effective address is outside the SS segment limit.
#GP(0) If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.

Real-Address Mode Exceptions

Exception Description
#UD If the LOCK prefix is used.
#NM CR0.EM[bit 2] or CR0.TS[bit 3] = 1.
#SS If a memory operand effective address is outside the SS segment limit.
#GP If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.

Protected Mode Exceptions

Exception Description
#UD If the LOCK prefix is used.
#AC(0) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
#PF(fault-code) If a page fault occurs.
#NM CR0.EM[bit 2] or CR0.TS[bit 3] = 1.
#SS(0) If a memory operand effective address is outside the SS segment limit.
#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.