x86 Instruction Set Reference

FLD - Load Floating Point Value

Opcode Mnemonic Description
D9 /0 FLD m32fp Push m32fp onto the FPU register stack.
DD /0 FLD m64fp Push m64fp onto the FPU register stack.
DB /5 FLD m80fp Push m80fp onto the FPU register stack.
D9 C0+i FLD ST(i) Push ST(i) onto the FPU register stack.
Description

Pushes the source operand onto the FPU register stack. The source operand can be in singleprecision, double-precision, or double extended-precision floating-point format. If the source operand is in single-precision or double-precision floating-point format, it is automatically converted to the double extended-precision floating-point format before being pushed on the stack.

The FLD instruction can also push the value in a selected FPU register [ST(i)] onto the stack.

Here, pushing register ST(0) duplicates the stack top.
Operation 
if(Source == ST(i)) Temporary = ST(i);
Top = Top - 1;
if(IsMemoryOperand(Source)) ST(0) = ConvertToExtendedDouble(Source);
else ST(0) = Temporary;
FPU flags affected

C1 Set to 1 if stack overflow occurred; otherwise, set to 0. C0, C2, C3 Undefined.

Floating-Point Exceptions
#ISStack overflow occurred.
#ISStack overflow occurred.
Protected Mode Exceptions
#DSource operand is a denormal value. Does not occur if the source operand is in double extended-precision floating-point format.
#DSource operand is a denormal value. Does not occur if the source operand is in double extended-precision floating-point format.
#GP(0)If destination is located in a non-writable segment. 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 is used to access memory and it contains a null segment selector.
#SS(0)If a memory operand effective address is outside the SS segment limit.
#NMEM or TS in CR0 is set.
#PF(fault-code)If a page fault occurs.
Real-Address Mode Exceptions
#GPIf a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#GPIf a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#SSIf a memory operand effective address is outside the SS segment limit.
Virtual-8086 Mode Exceptions
#GP(0)If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#GP(0)If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#SS(0)If a memory operand effective address is outside the SS segment limit.
#NMEM or TS in CR0 is set.
#PF(fault-code)If a page fault occurs.