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Double-precision Floating-point Instructions Section 3-15
Description LOGD(859) calculates the natural (base e) logarithm of the double-precision
(64-bit) floating-point number in words S to S+3 and places the result in words
D to D+3.
The source data must be positive; if it is negative, an error will occur and the
instruction will not be executed.
If the absolute value of the result is greater than the maximum value that can
be expressed as floating-point data, the Overflow Flag will turn ON and the
result will be output as
±∞.
Note The constant e is 2.718282.
The following diagram shows the relationship between the input data and
result.
Flags
Index Registers ---
Indirect addressing
using Index Registers
,IR0 to ,IR15
–2048 to +2047 ,IR0 to –2048 to +2047 ,IR15
DR0 to DR15, IR0 to IR15
,IR0+(++) to ,IR15+(++)
,–(– –)IR0 to, –(– –)IR15
Area S D
S+1 S →S+3 S+2 D+1 DD+3 D+2
log
e
R
S: Input data
R: Result
Name Label Operation
Error Flag ER ON if the source data is not recognized as floating-point
data.
ON if the source data is negative.
ON if the source data is not a number (NaN).
OFF in all other cases.
Equals Flag = ON if both the exponent and mantissa of the result are 0.
OFF in all other cases.
Overflow Flag OF ON if the absolute value of the result is too large to be
expressed as a double-precision (64-bit) floating-point
value.
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