Floating Point

The Arm® architecture provides high-performance and high-efficiency hardware support for floating-point operations in half-, single-, and double-precision arithmetic. It is fully IEEE-754 compliant with full software library support.

This page describes floating-support relative to Cortex®-A and Cortex-R processors. For information relative to Cortex-M, please refer to our DSP for Cortex-M page.

Key applications

The floating-point data type is essential for a wide range of digital signal processing (DSP) applications. Many applications inherently benefit from the dynamic range and precision of floating-point to deal with large data sets or data sets with unpredictable range. Then it makes floating-point usage particularly suitable when computational accuracy is a critical requirement.

Examples of such applications are:

  • Automotive control applications
    • Powertrain
    • ABS, Traction control & active suspension
  • 3D Graphics
    • Digital consumer products
    • Set-top boxes and games consoles
  • Imaging
    • Laser printers, still digital cameras, and digital video cameras
  • Industrial control systems
    • Motion controls

Specification

Armv8-A/R architecture

The Armv8 architecture supports single-precision (32-bit) and double-precision (64-bit) floating-point data types and arithmetic as defined by the IEEE 754 floating-point standard. It also supports the half-precision (16-bit) floating-point data type for data storage, by supporting conversions between single-precision and half-precision data types and double-precision and half-precision data types. When Armv8.2-FP16 is implemented, it also supports the half-precision floating-point data type for data-processing operations. 

The Advanced SIMD (NEON) instructions provide packed Single Instruction Multiple Data (SIMD) and single-element scalar operations, and support:

• Single-precision and double-precision arithmetic in AArch64 state.  

• Single-precision arithmetic only in AArch32 state.

• When Armv8.2-FP16 is implemented, half-precision arithmetic is supported in AArch64 and AArch32 states.

Floating-point support in AArch64 state SIMD is IEEE 754-2008 compliant with:

• Configurable rounding modes.

• Configurable Default NaN behavior.

• Configurable Flush-to-zero behavior.

Floating-point computation using AArch32 Advanced SIMD instructions remains unchanged from Armv7.

Scalable Vector Extension (SVE) for Armv8-A

SVE is the next-generation SIMD instruction set for AArch64 that introduces the architectural features for High Performance Computing (HPC). SVE extends the floating-point capability of the Armv8-A architecture targeting A64 ISA only.

Armv7-A/R and previous architectures

Prior to Armv8-A/R, the Arm architecture distinguishes between scalar (VFP) and Advanced SIMD extension (NEON™) floating-point support.

Up to Armv7-A/R architecture (included), floating-point architecture is a floating-point coprocessor extension to the instruction set architectures. For historic reasons, the Floating-point Extension is also called the VFP Extension.

 VFPv1 Obsolete. Details are available on request from Arm. 
 VFPv2 An optional extension to: * the Arm instruction set in the Armv5TE, Armv5TEJ, Armv6, and Armv6K architectures. * the Arm and Thumb instruction sets in the Armv6T2 architecture.
 VFPv3 An optional extension to the Arm, Thumb®, and ThumbEE instruction sets in the Armv7-A and Armv7-R profiles. VFPv3 can be implemented with either 32 or 16 doubleword registers. VFPv3U is a variant of VFPv3 that supports the trapping of floating-point exceptions to support code.
 VFPv3 with Half-precision Extension
 VFPv3 and VFPv3U can be extended by the optional Half-precision Extension, that provides conversion functions in both directions between half-precision floating-point and single-precision floating-point.
 VFPv4  

An optional extension to the Arm, Thumb, and ThumbEE instruction sets in the Armv7-A and Armv7-R profiles. VFPv4U is a variant of VFPv4 that supports the trapping of

floating-point exceptions to support code. VFPv4 and VFPv4U add both the Half-precision Extension and the fused multiply-add instructions to the features of VFPv3. VFPv4 can be implemented with either 32 or 16 doubleword registers.

The Armv7-A/R Advanced SIMD extension (NEON) offers single-precision floating-point support and performs IEEE 754 floating-point arithmetic with the following restrictions:

• Denormalized numbers are flushed to zero, see Flush-to-zero on page A1-51.

• Only default NaNs are supported

• The Round to Nearest rounding mode is used.

• Untrapped floating-point exception handling is used for all floating-point exceptions.

See section A1.4 Architecture extensions of Arm® Architecture Reference Manual Armv7-A and Armv7-R edition for a full description.

Related tools

Arm DS-5 Development Studio provides an end-to-end suite of tools for C/C++ software development for Arm-based platforms. DS-5 fully supports Arm floating-point architecture for programming and debugging.