Github user paul-rogers commented on the issue:
https://github.com/apache/drill/pull/517
Based on above discussion, I played around with the proposed solution. The
following takes into consideration the max precision of both the input and
output types. It DOES NOT handle truncation properly (but nor do any of the
other solutions.)
Here is the revised code:
if (precision.value <= 0) {
<#--
// since input precision is nonpositive, calculate precision
for this integer value
long precisionTmp = in.value == 0 ? 1 : in.value; // precision
for value 0 will be 1
int precisionCounter = 0;
while (precisionTmp != 0) {
++precisionCounter;
precisionTmp /= 10;
}
out.precision = precisionCounter;
-->
// Since precision is not provided, select one appropriate for
the
// largest integer value and the target decimal type.
// Note: if the integer is too large for the target precision,
silent
// truncation of the highest part of the number will occur.
This is
// obviously bad. What should happen is we shift scale and
discard
// the low-order digits.
// That is, if we convert 123,456,789,012 to Dec9, the result is
// 456,789,012 which is very obviously very wrong. It should be
// 123,456,789,000.
<#-- A correct solution requires a modification of the code
commented out above. -->
<#-- Precision needed by the largest from type value. -->
<#if type.from.equals( "Int" )>
<#assign inPrec = 10>
<#elseif type.from.equals( "BigInt" )>
<#assign inPrec = 19>
<#else>
<#-- Yes, create invalid syntax: that way the compiler will
tell us we missed a type. -->
<#assign inPrec = "Unexpected from type: ${type.from}">
</#if>
<#-- Maximum precision allowed by the to type. -->
<#if type.to.startsWith("Decimal9")>
<#assign maxPrec = 9>
<#elseif type.to.startsWith("Decimal18")>
<#assign maxPrec = 18>
<#elseif type.to.startsWith("Decimal28")>
<#assign maxPrec = 28>
<#elseif type.to.startsWith("Decimal38")>
<#assign maxPrec = 38>
<#else>
<#-- Yes, create invalid syntax: that way the compiler will
tell us we missed a type. -->
<#assign maxPrec = "Unexpected to type: ${type.to}">
</#if>
<#-- Note that this calculation is done here, rather than in
static variables,
because static members are not allowed for this function. -->
<#if inPrec < maxPrec>
// Maximum precision needed by the largest ${type.from} value.
out.precision = ${inPrec};
<#else>
// Maximum precision allowed by the ${type.to} type.
out.precision = ${maxPrec};
</#if>
}
else {
// since input precision is positive, assume it is correct, and
use it
out.precision = (int) precision.value;
out.scale = (int) scale.value;
}
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