himadripal commented on code in PR #7179:
URL: https://github.com/apache/arrow-rs/pull/7179#discussion_r2021953487
##########
arrow-cast/src/parse.rs:
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@@ -850,7 +850,16 @@ fn parse_e_notation<T: DecimalType>(
}
if exp < 0 {
- result = result.div_wrapping(base.pow_wrapping(-exp as _));
+ let result_with_scale = result.div_wrapping(base.pow_wrapping(-exp as
_));
+ let result_with_one_scale_up =
+ result.div_wrapping(base.pow_wrapping(-exp.add_wrapping(1) as _));
Review Comment:
`exp` in the `parse_e_notation` method is being overriden couple of times
based on which direction the decimal needs to shift and if the original string
has fractional in it. ( i.e 1.23e-2 has 2 fractional digits).
before this check, `exp` represents number of digits to be removed or added.
In this case, exp = -3
now, result_with_scale = 12
result_with_one_scale_up=123
to round up or down, we need to capture what is the digit next to last digit
in the result, in this case 3. How we get it is = (123 - 12* 10 )
if rounding_digit >=5 then we add +1 to the result
else result remains intact.
I added a debugging screenshot to help understand it more.
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