x86 Instruction Set Reference

FLD1/FLDL2T/FLDL2E/FLDPI/FLDLG2/FLDLN2/FLDZ

Load Constant

Opcode Mnemonic Description
D9 E8 FLD1 Push +1.0 onto the FPU register stack.
D9 E9 FLDL2T Push log_2(10) onto the FPU register stack.
D9 EA FLDL2E Push log_2(e) onto the FPU register stack.
D9 EB FLDPI Push pi onto the FPU register stack.
D9 EC FLDLG2 Push log_10(2) onto the FPU register stack.
D9 ED FLDLN2 Push log_e(2) onto the FPU register stack.
D9 EE FLDZ Push +0.0 onto the FPU register stack.
Description

Push one of seven commonly used constants (in double extended-precision floating-point format) onto the FPU register stack. The constants that can be loaded with these instructions include +1.0, +0.0, log_10(2), log_e(2), pi, log_2(10), and log_2(e). For each constant, an internal 66-bit constant is rounded (as specified by the RC field in the FPU control word) to double extendedprecision floating-point format. The inexact-result exception (#P) is not generated as a result of the rounding, nor is the C1 flag set in the x87 FPU status word if the value is rounded up.

See the section titled "Pi" in Chapter 8 of the IA-32 Intel Architecture Software Developer's Manual, Volume 1, for a description of the pi constant.
Operation 
Top = Top - 1;
ST(0) = Constant;
FPU flags affected

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

IA-32 Architecture Compatibility

When the RC field is set to round-to-nearest, the FPU produces the same constants that is produced by the Intel 8087 and Intel 287 math coprocessors.

Floating-Point Exceptions
#ISStack overflow occurred.
Protected Mode Exceptions
#NMEM or TS in CR0 is set.
Real-Address Mode Exceptions
#NMEM or TS in CR0 is set.
Virtual-8086 Mode Exceptions
#NMEM or TS in CR0 is set.