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TECHNICAL REPORT
5G;
Update to fixed-point basic operators
(3GPP TR 26.973 version 15.0.0 Release 15)
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3GPP TR 26.973 version 15.0.0 Release 15 1 ETSI TR 126 973 V15.0.0 (2018-07)
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3GPP TR 26.973 version 15.0.0 Release 15 2 ETSI TR 126 973 V15.0.0 (2018-07)
Intellectual Property Rights
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Foreword
This Technical Report (TR) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
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Modal verbs terminology
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"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
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Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 4
Introduction . 4
1 Scope . 5
2 References . 5
3 Abbreviations . 5
4 Extension to the STL2009 Basic Operators . . 5
4.1 Analysis of the gap between current basic operators and modern DSP architectures . 5
4.2 Test methodology for validating the extended basic operators . 6
4.2.0 General . 6
4.2.1 Test methodology . 7
4.2.2 Test results for basic operator Mpy_32_16_1 . 8
4.2.3 Test results . 12
4.2.4 Test results conclusion . 12
5 Alternative EVS Implementation Using the Extended Basic Operators . 13
5.1 Merits of an alternative EVS implementation using the extended basic operators. 13
5.2 Example pseudo code to illustrate some of the benefits of modern DSP architectures . 15
5.3 Validation of an alternative EVS implementation using updated basic operators . 17
5.3.1 C-code inspection . 17
5.3.2 Objective performance evaluation of the alternative EVS implementation . 17
5.3.3 Subjective performance evaluation of the alternative EVS implementation . 18
6 Conclusions . 19
Annex A: Extended Basic Operators . 21
A.1 Basic operators that use 64 bit registers/accumulators . 21
A.2 Basic operators which use 32 bit precision multiply . 26
A.3 Basic operators which use complex data types . 32
A.4 Basic operators for control operation . 40
Annex B: Weights of the STL basic operators . 41
Annex C: Change history . 46
History . 47
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Foreword
This Technical Report has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
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3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
Introduction
The last major update to the ITU-T Basic Operators [6] was in 2005, with a follow on update in 2009. These basic
operators serve as a foundation for reference software of codecs specified by 3GPP. During the last several years,
processors with wide accumulators, and support for single-instruction-multiple-data (SIMD), and very long instruction
word (VLIW) features have become prevalent. The basic operators of 2009 now need to be extended to leverage these
capabilities of modern processors so that implementations with lower mega-cycles-per-second (MCPS) and lower-
power may be realized.
Enhanced Voice Services (EVS) is one of the recent codecs defined by 3GPP that can leverage these features of modern
processors. The existing EVS reference software would have to be appropriately modified to leverage these extended
basic operators without changing the underlying algorithm. This is referred to as an alternative EVS implementation
using the extended basic operators.
This alternative EVS implementation would have to be evaluated to ensure that inter-operability is maintained in
addition to ensuring that voice quality is not impacted.
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1 Scope
The present document covers the following topics:
1) Assessment of the gaps between modern processors and the existing set of basic operators (STL2009) [6].
2) Proposal of an extended set of operators addressing modern DSP architectures as an extension to STL2009.
3) Assessment of merits of an alternative EVS implementation using extended STL2009 Basic Operators.
4) Proposal for validation of an alternative EVS implementation using extended STL2009 Basic Operators.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 26.442: "Codec for Enhanced Voice Services (EVS); ANSI C code (fixed-point)".
[3] Recommendation ITU-T P.800 (08/1996): "Methods for subjective determination of transmission
quality".
[4] Recommendation ITU-T P.863 (09/2014): "Perceptual objective listening quality assessment".
[5] 3GPP TS 26.443: "Codec for Enhanced Voice Services (EVS); ANSI C code (floating-point)".
[6] Recommendation ITU-T G.191 (03/10): "Software tools for speech and audio coding
standardization".
[7] 3GPP TR 26.952: "Codec for Enhanced Voice Services (EVS); Performance Characterization
(Release 14)".
3 Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
3GPP TR 21.905 [1].
SIMD Single Instruction Multiple Data
STL Software tools for speech and audio coding standardization
VLIW Very Long Instruction Word.
4 Extension to the STL2009 Basic Operators
4.1 Analysis of the gap between current basic operators and
modern DSP architectures
State-of-the-art processor architectures, such as the recent ones from Intel, ARM, QUALCOMM, Texas Instruments
etc., support wide accumulators, SIMD and VLIW capabilities. The last major update to the ITU-T Basic Operators was
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in 2005, with a follow on update in 2009 [6]. It appears that these earlier versions of the Basic Operators (2009 and
earlier) were influenced by older DSP architectures such as the Texas Instruments TMS320C5x and TMS320C54x
processors where the accumulator was 40 bits wide.
However, a survey of the state-of-the-art processor architectures shows that most of them support the following
capabilities:
- Wider (64 bit) accumulators and registers.
- Wider accumulators enable additional guard bits which eliminate the need for checking for saturation after every
basic operation.
- SIMD (Single Instruction Multiple Data) instructions which can process vector data. For example, a single
instruction can process two 32-bit data elements or four 16-bit elements in parallel.
- VLIW (Very Long Instruction Word) enables several operations to be executed in parallel in a single cycle.
Basic operators that are friendlier to compilers, and enable SIMD and VLIW features to be leveraged, can significantly
reduce implementation time. Improved compiler technology and software development tools interpret data types and
associated basic operators to map them to a processor architecture for better Out-of-box (OOB) performance. Without
this computer assisted optimization, an engineer would have to hand-optimize the code which would result in increased
engineering effort and longer time to market.
Many recent audio/hybrid codecs make extensive use of 16bit x 32bit MAC (multiply and accumulate) and 32bit x
32bit MAC operations which are realized quite differently between VLIW and SIMD architectures and the current
Basic Operators:
- Current STL2009 Basic operators require saturation and truncation after every multiply-accumulate (MAC)
operation to maintain bit-exactness.
- The current Basic operator saturation checks prevent use of SIMD parallelism.
- To maintain bit-exactness, cycles are wasted resulting in higher MCPS and power on VLIW and SIMD capable
devices.
- Higher precision variables, such as 64bit operands, are partitioned into smaller width operands, processed and
then put back to the original width. This results in an overhead and processor cycles are wasted.
Considering the capabilities of modern processor architectures, as well as the characteristics of the latest speech and
audio codecs, there is a need for extending STL2009 with additional basic operators & data types to better leverage the
capabilities of state-of-the-art processor architectures and characteristics of DSP algorithms.
4.2 Test methodology for validating the extended basic
operators
4.2.0 General
This clause describes a test framework that will compare the fixed-point arithmetic accuracy of the extended basic
operators against a floating-point implementation of the extended basic operators. Each basic operator will be tested for
4 different data patterns.
In table 1 below, the extended basic operators have been classified into four main classes. The test patterns used for
testing and the build options of the test framework are also shown below.
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Table 1: Classification of the extended basic operators
Test framework for extended basic operators
Main class Subclass Total basops Covered basops
64-bit Integer Mac 4 4
64-bit Mac 7 7
64-bit Math 12 12
64-bit scale 7 7
64 bit accumulator 64-bit move 5 0
Complex Math 7 7
Complex Mac 9 9
Complex Move 10 0
Complex Complex Scale 9 9
32*16 bit Enh MAC 6 6
Enhanced 32 bit 32*32 bit Enh MAC 6 6
Control code ops 18 0
Total 100 67
Test data patterns:
- -1.0 to 1.0 float range with configurable interval.
- Random numbers.
- Special values: very low level values (e.g., in the range of 1e-3, 1e-6 etc.), nominal and large values
- Custom mode: users can specify their customized array of size N.
Build options:
MSVC 2017 and MSVC 2013 workspaces are provided, with 2 options:
- MSVC 2017/2013 project.
- Gcc based makefiles.
4.2.1 Test methodology
In Figure 1 below, a block diagram explains how to validate the extended STL2009 Basic Operators implementation
against a reference floating-point implementation. A data generator generates floating-point notation data values that are
then converted into fixed-point notation and these are input to the design under test (DUT) implementation of the
extended STL2009 Basic Operators implementation. The same fixed-point data is converted into floating-point
notation, and then input to a reference floating-point implementation of the extended STL2009 Basic Operators. The
fixed-point output of the DUT is converted to floating-point notation, and then compared against the reference floating-
point implementation output and an error value is generated and logged.
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Figure 1: Block diagram illustrating how the fixed-point implementation is validated against a
floating-point reference implementation of the extended STL2009 basic operators
In the following clauses, the test results for an example basic operator, Mpy_32_16_1 are reported.
4.2.2 Test results for basic operator Mpy_32_16_1
The setup in figure 1 was used for testing with four different types of data:
1) Random input numbers
2) A sweep from a negative number to a positive number
3) A piecewise sweep from a negative number to a positive number
4) A custom input where a user can specify an array of size N with custom inputs
Figures 2, 3, 4 and 5 illustrate the results of the test for the above four different data types. The error between the fixed-
point implementation and floating-point implementation are extremely small thereby validating the fixed-point
implementation.
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Figure 2: Test results for basic operator Mpy_32_16_1 using random input. The error between the
fixed-point output and floating-point output is very small.
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Figure 3: Test results for basic operator Mpy_32_16_1 using a sweep input. The error between the
fixed-point output and floating-point output is very small.
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Figure 4: Test results for basic operator Mpy_32_16_1 using a piecewise sweep input. The error
between the fixed-point output and floating-point output is very small.
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Figure 5: Test results for basic operator Mpy_32_16_1 using a user defined custom input. The error
between the fixed-point output and floating-point output is very small.
4.2.3 Test results
For a complete report of the framework used, as well as the results of the test, please see the attachment
"TestResultsAndTestFrameworkOfExtendedBASOPValidation.zip"
This attachment has four zipped files as described below:
- "Baseop_tst_frmwork.zip" – Test framework package. For details of this package, and how to run it, please see
the README file in the zipped package. For a summary of the results and the details of the test setup, please see
the excel file "Tst_framework.xlsx" available inside the "doc" folder of this zipped package.
- "precision_abs_err_report.csv" details the test results and reports the average and bits-in-error summary for all
the 67 basic operators.
- "W_mult_32_32.xlsx" shows the details of the test for this example basic operator.
- "Mpy_32_16_1.xlsx" shows the details of the test for this example basic operator.
4.2.4 Test results conclusion
Based on the results reported in "precision_abs_err_report.csv", it can be concluded that the fixed-point implementation
of the extended basic operators all pass against the reference floating-point implementation of the same extended basic
operators.
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5 Alternative EVS Implementation Using the Extended
Basic Operators
5.1 Merits of an alternative EVS implementation using the
extended basic operators
EVS [2] is a sophisticated hybrid audio-speech codec with several modes of operation. As such it has a large number of
functions. Manually optimizing this large set of functions is prohibitive from an effort (and therefore time) perspective.
Implementers will have to rely on computer assisted tools and compiler to get them as close to a final implementation as
possible, and spend the last mile in manual optimization to reach the final target performance. It is therefore imperative
that the basic operators are defined in such a manner that they lend themselves to better leverage the features and
capabilities of modern DSP architectures. Data types need to be mapped to match the processor registers or operand
widths of data used in SIMD (Single Instruction Multiple Data) processing; basic operators need to be mapped to
processor instructions. A standard reference C code written with these aspects in mind will result in an implementation
that leverages SIMD and VLIW (Very Long Instruction Word) features of the processor better and results in an out-of-
the-box (OOB) performance that is quite close to the final desired performance. The compiler can optimize the code
across all the files and functions thereby significantly reducing manual optimization effort. Implementers can go to
market faster.
Figure 6 shows the benefits of creating an alternate reference C code for EVS using the updated basic operator:
1) Reduced hand-optimization efforts lead to reduced total engineering effort, and hence improved time to market.
2) Improved MCPS numbers in OOB and final hand-optimized code.
3) Reduced code size. Reduced MCPS and memory reduces overall power used. This should facilitate extended
battery life.
Figure 6: Benefits of proposed alternate reference C for EVS
Using the existing standard EVS Reference code version 14.0.0 as a starting point, an alternative C code that leverages
the proposed basic operators has been created. During this creation process, step by step, several key parameters have
been monitored such as the engineering effort spent expressed as time (days, weeks, months), and corresponding
reduction in MCPS.
Figure 7 shows the optimization level achieved versus engineering effort measured in units of time. As the figure
shows, the OOB performance of the existing reference C is at 269 MCPS, while the OOB performance of the proposed
alternative EVS reference C code is at 162 MCPS. This is a gain of 1.66x achieved in matter of a few days of
engineering effort. Next, time is spent restructuring the code and hand optimizing. The final hand-optimized version is
at 61.9 MCPS compared to 77.5 MCPS for the existing EVS reference implementation. This is a gain of 1.25x.
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Figure 7: Impact of alternate reference C at different phases of the implementation process
In table 2, the improvement in weighted million operations per second (WMOPS) of the alternative EVS
implementation using extended basic operators is compared against the WMOPS of the existing EVS standard reference
code using STL2009 basic operators as a baseline. Second row shows a benefit of 1.07x with changing the weights for
STL2009 basic operators. Third row shows the total benefit of 1.17x with the use of the extended basic operators and
weight change of the existing STL2009 basic operators.
Table 2: WMOPS based Comparison of the alternative EVS implementation with existing EVS
implementation
Average WMOPS
EVS Code Base - STL_basops complexity
Improvement
Encoder Decoder Total
14.0.0 weights
Over Reference
Reference with
STL2009 weights as is
STL2009 53.3 24.2 77.5 1.00x
Reference with With new proposed weights for
STL2009 STL2009 50.6 22.1 72.7 1.07x
With new proposed weights for
Alternate Reference
STL2009 & for extended basic
with STL2017
operators 47.1 18.9 66 1.17x
Following test cases were used for WMOPS and MCPS calculation:
- Encoder test case: -rf HI 3 13200 32 stv32n2.INP stv32n2_rfHI3_13200_32kHz.COD
- Decoder test case: 32 stv32c_rfHI3_13200_32kHz.COD stv32c_rfHI3_13200.out
The WMOPS numbers reported in Table1 are average WMOPS for this worst case complexity test vector. Please refer
to 3GPP TR 26.952: Codec for Enhanced Voice Services (EVS); Performance Characterization (Release 14) [7], for a
more detailed explanation of WMOPs for EVS.
In table 3, the improvement in million cycles per seconds (MCPS) of the alternative EVS implementation is compared
against the MCPS of the existing EVS standard reference code on a specific DSP platform using STL2009 basic
operators as a baseline. A gain of 1.25x is observed.
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The gain in final MCPS of 1.25x is significantly more than gain of 1.17x in WMOPS. The explanation is that the
existing method of computing WMOPS does not address the cycles gained with VLIW where multiple instructions are
executed in parallel. In addition, the current assigned integer weights of 1 or higher for SIMD and VLIW friendly
instructions does not account for the inherent parallelism possible of processing multiple operands in a single cycle in
modern processors.
Table 3: MCPS based Comparison of the alternative EVS implementation with existing EVS
implementation on a Cadence Tensilica HiFi DSP
ALT_REFC with
REFC with STL2009
STL2017
Perf parameter Performance improvement
Total (Enc + Dec) Total (Enc + Dec)
OOB MCPS 269.3 162.5 1.66x
Final MCPS 77.5 61.9 1.25x
Code size – OOB (in K
2117.3 2036.6 1.04x
Bytes)
5.2 Example pseudo code to illustrate some of the benefits of
modern DSP architectures
The following examples illustrate the benefits of VLIW and SIMD features of modern DSP architectures. The existing
reference code needs to be changed to leverage the extended basic operators that exploit the features of modern DSP
architectures. The following examples with pseudo code show that cycles are reduced from 4 to 2.
Example 1:
Original Reference C Code –
for (i=0: i {
acc = acc + a[i]*b[i]; /* multiply, truncate, and saturate are happening */
}
/* Regular implementation */
/* Multiply, truncate, and saturate are happening for each element. */
/* Truncate and saturate here imply that order of execution is important. Compiler cannot change this order of execution
without violating bit-exactness */
Int_32 acc;
acc = a[0]*b[0]; /* cycle 1 */
acc = acc + a[1]*b[1]; /* cycle 2 */
acc = acc + a[2]*b[2]; /* cycle 3 */
acc = acc + a[3]*b[3]; /* cycle 4 */
/* total cycles
...