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3-344 Vol. 2A FLD1/FLDL2T/FLDL2E/FLDPI/FLDLG2/FLDLN2/FLDZ—Load Constant
INSTRUCTION SET REFERENCE, A-M
FLD1/FLDL2T/FLDL2E/FLDPI/FLDLG2/FLDLN2/FLDZ—Load Constant
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
2
10, log
2
e, π, log
10
2, and log
e
2. For each
constant, an internal 66-bit constant is rounded (as specified by the RC field in the
FPU control word) to double extended-precision 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 Intel® 64 and IA-32 Architectures Soft-
ware Developer’s Manual, Volume 1, for a description of the π constant.
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
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.
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.
Opcode* Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
D9 E8 FLD1 Valid Valid Push +1.0 onto the FPU register stack.
D9 E9 FLDL2T Valid Valid Push log
2
10 onto the FPU register stack.
D9 EA FLDL2E Valid Valid Push log
2
e onto the FPU register stack.
D9 EB FLDPI Valid Valid Push π onto the FPU register stack.
D9 EC FLDLG2 Valid Valid Push log
10
2 onto the FPU register stack.
D9 ED FLDLN2 Valid Valid Push log
e
2 onto the FPU register stack.
D9 EE FLDZ Valid Valid Push +0.0 onto the FPU register stack.
NOTES:
* See IA-32 Architecture Compatibility section below.