Mne- Op Name monic Characteristics Code ADD NORMALIZED (extended) AXR RR C XP SP EU EO LS 36
ADD NORMALIZED (long) ADR RR C FP SP EU EO LS 2A
ADD NORMALIZED (long) AD RX C FP A SP EU EO LS 6A
ADD NORMALIZED (short) AER RR C FP SP EU EO LS 3A
ADD NORMALIZED (short) AE RX C FP A SP EU EO LS 7A
ADD UNNORMALIZED (long) AWR RR C FP SP EO LS 2E
ADD UNNORMALIZED (long) AW RX C FP A SP EO LS 6E
ADD UNNORMALIZED (short) AUR RR C FP SP EO LS 3E
ADD UNNORMALIZED (short) AU RX C FP A SP EO LS 7E COMPARE (long) CDR RR C FP SP 29 COMPARE (long) CD RX C FP A SP 69 COMPARE (short) CER RR C FP SP 39 COMPARE (short) CE RX C FP A SP 79
DIVIDE (long) DDR RR FP SP EU EO FK 2D
DIVIDE (long) DD RX FP A SP EU EO FK 6D
DIVIDE (short) DER RR FP SP EU EO FK 3D
DIVIDE (short) DE RX FP A SP EU EO FK 7D
HALVE (long) HDR RR FP SP EU 24
HALVE (short) HER RR FP SP EU 34 LOAD (long) LDR RR FP SP 28 LOAD (long) LD RX FP A SP 68 LOAD (short) LER RR FP SP 38 LOAD (short) LE RX FP A SP 78 LOAD AND TEST (long) LTDR RR C FP SP 22 LOAD AND TEST (short) LTER RR C FP SP 32 LOAD COMPLEMENT (long) LCDR RR C FP SP 23 LOAD COMPLEMENT (short) LCER RR C FP SP 33 LOAD NEGATIVE (long) LNDR RR C FP SP 21 LOAD NEGATIVE (short) LNER RR C FP SP 31 LOAD POSITIVE (long) LPDR RR C FP SP 20 LOAD POSITIVE (short) LPER RR C FP SP 30 LOAD ROUNDED (ext. to long) LRDR RR XP SP EO 25 LOAD ROUNDED (long to short) LRER RR XP SP EO 35 MULTIPLY (extended) MXR RR XP SP EU EO 26 MULTIPLY (long) MDR RR FP SP EU EO 2C MULTIPLY (long) MD RX FP A SP EU EO 6C MULTIPLY (long to extended) MXDR RR XP SP EU EO 27 MULTIPLY (long to extended) MXD RX XP A SP EU EO 67 MULTIPLY (short to long) MER RR FP SP EU EO 3C l'1UL TIPL Y (short to long) ME RX FP A SP EU EO 7C STORE (long) STD RX FP A SP ST 60 STORE (short) STE RX FP A SP ST 70 SUBTRACT NORMALIZED (ext.) SXR RR C XP SP EU EO LS 37 SUBTRACT NORMALIZED (long) SDR RR C FP SP EU EO LS 2B SUBTRACT NORMALIZED (long) SD RX C FP A SP EU EO LS 6B SUBTRACT NORMALIZED (short) SER RR C FP SP EU EO LS 3B SUBTRACT NORMALIZED (short) SE RX C FP A SP EU EO LS 7B SUBTRACT UNNORMALIZED (long) SWR RR C FP SP EO LS 2F SUBTRACT UNNORMALIZED (long) Sl.J RX C FP A SP EO LS 6F SUBTRACT UNNORMALIZED (short) SUR RR C FP SP EO LS 3F SUBTRACT UNNORMALIZED (short) SU RX C FP A SP EO LS 7F
Summary of Floating-Point Instructions (Part 1 of 2) Chapter 9. Floating-Point Instructions 9-5
Explanation:
A Access exceptions for logical addresses.
C Condition code is set.
EO Exponent-overflow exception.
EU Exponent-underflow exception.
FK Floating-point-divide exception. FP Floating-point facility. LS Significance exception.
RR RR instruction format.
RX RX instruction format. SP Specification exception.
ST PER storage-alteration event. XP Extended-precision floating-point facility.
Summary of Floating-Point Instructions (Part 2 of 2)
ADD NORMALIZED
AER R 1 ,R 2 [RR, Short Operands]
'3A' I R t I R2 0 8 12 15
AE Rl'D
2
(X
2
,B
2
)
[RX, Short Operands]
'7A' I R t I X
2 I B2 I D2 0 8 12 16 20 31
ADR R t ,R
2
[RR, long Operands]
'2A' I R 1 I R 2 o 8 12 15
AD [RX, long Operands]
'6A'
o 8 12 16 20 31
AXR R 1 ,R
2
[RR, Extended Operands]
'36' I Rl I R2 I o 8 12 15
The second operand is added to the first
operand, and the normalized sum is
placed at the first-operand location.
Addition of two floating-point numbers
consists in characteristic comparison,
fraction alignment, and signed fraction
addition. The characteristics of the
two operands are compared, and the frac­ tion accompanying the smaller
characteristic is aligned with the other
fraction by a right shift, with its
9-6 System/370 Principles of Operation
characteristic increased by one for each
hexadecimal digit of shift until the two
characteristics agree.
When a fraction is shifted right during
alignment, the leftmost hexadecimal
digit shifted out is retained as a guard
digit. The fraction that is not shifted
is considered to be extended with a zero
in the guard-digit position. When no
alignment shift occurs, both operands
are considered to be extended with zeros
in the guard-digit position. The frac­
tions with signs are then added
algebraically to form a signed interme­
diate sum.
The intermediate-sum fraction consists
of seven (short format), 15 (long
format), or 29 (extended format) hexade­
cimal digits, including the guard digit,
and a possible carry. If a carry is
present, the sum is shifted right one
digit position so that the carry becomes
the leftmost digit of the fraction, and
the characteristic is increased by one.
If the addition produces no carry, the
intermediate-sum fraction is shifted
left as necessary to eliminate any lead­
ing hexadecimal zero digits resulting
from the addition, provided the fraction
is not zero. Zeros are supplied to the
vacated rightmost digits, and the char­
acteristic is reduced by the number of
hexadecimal digits of shift. The frac­
tion thus normalized is then truncated
on the right to six (short format), 14
(long format), or 28 (extended format)
hexadecimal digits. In the extended
format, a characteristic is generated
for the low-order part, which is 14 less
than the high-order characteristic.
The sign of the sum is determined by the
rules of algebra, unless all digits of
the intermediate-sum fraction are zero,
in which case the sign is made plus.
An exponent-overflow exception is recog­
nized when a carry from the leftmost
position of the intermediate-sum frac­
tion would cause the characteristic of
the normalized sum to exceed 127. The
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