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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
gx_02.fm.(1.2)
March 27, 2006
Programming Model
Page 105 of 377
Table 2-24 summarizes the single-precision and double-precision floating-point store and stfiwx instructions.
Some floating-point store instructions require conversions in the LSU. Table 2-25 shows conversions the LSU
makes when executing a Store Floating-Point Single instruction.
Note: The FPRs are not initialized by HRESET
, and they must be initialized with some valid value after POR
HRESET
and before being stored.
Table 2-26 shows the conversions made when performing a Store Floating-Point Double instruction. Most
entries in the table indicate that the floating-point value is simply stored. Only in a few cases are any other
actions taken.
Table 2-24. Floating-Point Store Instructions
Name Mnemonic Syntax
Store Floating-Point Single stfs frS,d(rA)
Store Floating-Point Single Indexed stfsx frS,rB
Store Floating-Point Single with Update stfsu frS,d(rA)
Store Floating-Point Single with Update Indexed stfsux frS,rB
Store Floating-Point Double stfd frS,d(rA)
Store Floating-Point Double Indexed stfdx frS,rB
Store Floating-Point Double with Update stfdu frS,d(rA)
Store Floating-Point Double with Update Indexed stfdux frS,rB
Store Floating-Point as Integer Word Indexed
1
stfiwx frS,rB
1. The stfiwx instruction is optional in the PowerPC Architecture.
Table 2-25. Store Floating-Point Single Behavior
FPR Precision Data Type Action
Single Normalized Store
Single Denormalized Store
Single Zero, infinity, QNaN Store
Single SNaN Store
Double Normalized
If (exp ð ≤ 896)
then Denormalize and Store
else
Store
Double Denormalized Store zero
Double Zero, infinity, QNaN Store
Double SNaN Store
Table 2-26. Store Floating-Point Double Behavior (Page 1 of 2)
FPR Precision Data Type Action
Single Normalized Store
Single Denormalized Normalize and Store
Single Zero, infinity, QNaN Store