ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

VFP Vector Operation Support
F.1 About VFP vector mode
The single-precision registers can be used to hold short vectors of up to 8 single-precision values. Arithmetic
operations on all the elements of such a vector can be specified by just one single-precision arithmetic
instruction.
Similarly, the double-precision registers can be used to hold short vectors of up to 4 double-precision values,
and double-precision arithmetic instructions can specify operations on these vectors.
A vector consists of 2-8 registers from a single bank. VFP register banks on page AppxF-5 describes the
division of the VFP register set into banks.
The FPSCR.LEN field controls the number of elements in a vector. The register number in the instruction
specifies the register that contains the first element of the vector. The FPSCR.STRIDE field controls the
increment between the register numbers of the elements of the vector. If the total increment causes the
register number to overflow the top of a register bank, the register number wraps around to the bottom of
the bank, as shown in VFP register banks on page AppxF-5.
For details of the FPSCR.LEN and FPSCR.STRIDE fields see Vector length and stride control on
page AppxF-3.
A VFP instruction can operate on:
operand vectors with LEN elements, producing a result vector with LEN elements
an operand vector with LEN elements and a scalar operand, producing a result vector with LEN
elements
scalar operands, producing a scalar result.
These three operation types are identical if LEN == 1.
To control which type of operation an instruction performs, you choose the registers for the instruction from
different register banks. VFP instruction type selection on page AppxF-7 describes how to select the
instruction type.
F.1.1 Affected instructions
The following VFP instructions are affected by VFP vector mode:
VABS VADD VDIV VMLA VMLS
VMOV (immediate) VMOV (register) VMUL VNEG VNMLA
VNMLS VNMUL VSQRT VSUB
All other VFP instructions behave as described in their instruction descriptions regardless of the values of
FPSCR.LEN and FPSCR.STRIDE.
AppxF-2 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B