Multiply And Add Facility; Elementary Math Library Facility; Square Root Facility And Mathematical Function Facility - IBM 4381 Manual

Multiply and Add Facility
The standard Multiply and Add Facility for all uniprocessor 4381 model groups
provides the MULTIPLY AND ADD instruction and is functional in System/370
and System/370-XA modes. This instruction performs a combination of vector
multiplication and addition operations that can replace the inner loop of common
matrix computations to improve the performance of the multiply and add
operations (up to 35% reduction in compute-intensive subroutine execution time).
The MULTIPLY AND ADD instruction performs the function A
=
(B x S)
+
C
where A, B, and C are vectors and S is a scalar. A, B, and S must consist of
normalized, long-format floating-point numbers, while vector C can contain
unnormalized, long-format elements.
A common use for this assist is to have an installation-written Assembler Language
routine containing this instruction called from high-level language programs as
required. The MADS mnemonic is supported by the Assembler Language. For
detailed information about this instruction, see IBM System/ 3 70 Mathematical
Assists (SA22-7094 ).
Elementary Math Library Facility
The Elementary Math Library Facility feature is standard in the 4381 Processor
Model Group 2. It is functional in System/370 and System/370-XA modes. It
provides four functions (eight instructions) that use short- and long-format
floating-point operands. The instructions are SQUARE ROOT (SQDR and
SQER), EXPONENTIAL (EXPD and EXPE), COMMON LOGARITHM
(LGCD and LGCE), and NATURAL LOGARITHM (LGND and LGNE). The
two operands are contained in floating-point registers.
The Elementary Math Library (EML) Programming RPQ (5799-BTB) for VS
FORTRAN Mathematical Library supports this facility for operation under
VM/CMS, MVS/370, and MVS/XA. This assist can reduce processor-busy time
by
up to 64 percent for the assisted functions.
The publication IBM System/ 3 70 Mathematical Assists (SA22-7094) describes the
Elementary Math Library Facility instructions.
Square Root Facility and Mathematical Function Facility
These two features provide the functions included in the Elementary Math Library
Facility for the 4381 Model Group 2. The Square Root Facility is standard in all
4381 uniprocessor model groups and performs an assist for the square root
function using long- or short-precision floating-point arithmetic.
The Mathematical Function Facility is standard in 4381 Model Groups 12 and 13
to assist in exponential, common logarithms, and natural logarithm functions using
short- or long-format floating point arithmetic. Reductions in compute-intensive
subroutine execution time vary from 37% to 64% using this facility.
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A Guide to the IBM 4381 Processor