Instruction Syntax

Mnemonic	Format	Flags
fabs	frD,frB	Rc = 0
fabs.	frD,frB	Rc = 1

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	111111 (0x3F)
frD	6-10	Destination floating-point register
Reserved	11-15	00000
frB	16-20	Source floating-point register B
Reserved	21	0
XO	22-30	100001000 (264)
Rc	31	Record Condition Register

Operation

frD ← |frB|

The absolute value of the contents of floating-point register frB is placed into floating-point register frD. The operation is performed by clearing the sign bit of frB.

Note: This instruction does not affect the floating-point status and control register (FPSCR) exception bits, but may affect the FPSCR condition code bits if Rc = 1.

Affected Registers

Floating-Point Status and Control Register (FPSCR)

(if Rc = 1)

• FPRF (Floating-Point Result Flags) - updated to reflect the result

For more information on floating-point status see Section 2.1.4, "Floating-Point Status and Control Register (FPSCR)," in the PowerPC Microprocessor Family: The Programming Environments manual.

Examples

Basic Absolute Value

lfd f1, negative_value(r0)  # Load negative floating-point value
fabs f2, f1                 # f2 = |f1| (absolute value)
# f2 now contains the positive absolute value

Absolute Value with Condition Recording

lfd f3, input_value(r0)     # Load floating-point input
fabs. f4, f3               # f4 = |f3|, set FPSCR condition codes
# FPSCR condition codes now reflect the result

Distance Calculation

# Calculate absolute difference between two values
lfd f1, value_a(r0)        # Load first value
lfd f2, value_b(r0)        # Load second value
fsub f3, f1, f2            # f3 = f1 - f2
fabs f4, f3                # f4 = |f1 - f2| (absolute difference)

Vector Magnitude Component

# Calculate absolute values for vector components
lfd f1, x_component(r0)    # Load X component
lfd f2, y_component(r0)    # Load Y component
lfd f3, z_component(r0)    # Load Z component
fabs f1, f1                # |X|
fabs f2, f2                # |Y|
fabs f3, f3                # |Z|
# Now ready for magnitude calculation

Sign Removal

# Ensure all values are positive
lfd f1, data_array(r3)     # Load array element
fabs f1, f1                # Remove sign bit
stfd f1, data_array(r3)    # Store back positive value

Floating-Point Comparison Helper

# Use absolute value in comparisons
lfd f1, threshold(r0)      # Load threshold value
lfd f2, measured_value(r0) # Load measured value
fabs f2, f2                # Get absolute value of measurement
fcmpo cr0, f2, f1          # Compare |measured| with threshold
blt below_threshold        # Branch if |measured| < threshold

Related Instructions

fnabs, fneg, fmr, fcmpo