Allow log/pow on negative scale decimals

Is your feature request related to a problem or challenge?

#17023 introduced handling of decimals for log natively; previously we'd cast the input to float before performing the log.

It introduced a condition against negative scale decimals, as the implementation couldn't yet handle them. This is technically a regression as previously we could handle them via casting to float before doing the log.

Describe the solution you'd like

Short term solution: for negative scale decimals, cast to float to perform log

Long term/proper solution: improve decimal log code to handle negative scales

Additional context

Same for pow: #18032

take

@Jefffrey

@Jefffrey please review .

Fix regression for negative-scale decimal128 in log (#19315)

Still pending:

power
log for decimal32/64 after recent PR: feat: Support log for Decimal32 and Decimal64 #18999

@Jefffrey

Hey @Jefffrey i have opened another PR , please review . Also i am not sure if the calculation shown in example doc for power function at datafusion/functions/src/math/power.rs is correct ?

``text the example doc
/// b^e * 10^(-s * e) * 10^s = b^e / 10^(s * (e-1))
/// ```
/// Example of 2.5 ^ 4 = 39:
/// 2.5 is represented as 25 with scale 1
/// The unscaled result is 25^4 = 390625
/// Scale it back to 1: 390625 / 10^4 = 39

added support for negative scale for log decimal32/64 and power (#19409)

Now that we have merged the following PRs, shall we close this one?

I think there are still some checks to fix from a cursory glance at the code:

datafusion/datafusion/functions/src/utils.rs

Lines 202 to 206 in f1e5c94

    
           if scale < 0 { 
        
               Err(ArrowError::ComputeError( 
        
                   "Negative scale is not supported".into(), 
        
               )) 
        
           } else if scale == 0 {

datafusion/datafusion/functions/src/utils.rs

Lines 219 to 223 in f1e5c94

    
           if scale < 0 { 
        
               Err(ArrowError::ComputeError( 
        
                   "Negative scale is not supported".into(), 
        
               )) 
        
           } else if scale == 0 {

datafusion/datafusion/functions/src/utils.rs

Lines 236 to 240 in f1e5c94

    
           if scale < 0 { 
        
               Err(ArrowError::ComputeError( 
        
                   "Negative scale is not supported".into(), 
        
               )) 
        
           } else if scale == 0 {

@Jefffrey

Thanks @Jefffrey -- I was asking because this issue is (rightly) listed as needed for the 52.0.0 release, which we are gearing up for next week. @shifluxxc do you think you will have time to complete the rest of the work? Maybe even writing some .slt tests that show the current behavior / errors would be valuable

@alamb

@alamb i will try to raise a PR today itself addressing these issues, Thank you .

I think there are still some checks to fix from a cursory glance at the code:

datafusion/datafusion/functions/src/utils.rs

Lines 202 to 206 in f1e5c94
if scale < 0 {
Err(ArrowError::ComputeError(
"Negative scale is not supported".into(),
))
} else if scale == 0 {

datafusion/datafusion/functions/src/utils.rs

Lines 219 to 223 in f1e5c94
if scale < 0 {
Err(ArrowError::ComputeError(
"Negative scale is not supported".into(),
))
} else if scale == 0 {

datafusion/datafusion/functions/src/utils.rs

Lines 236 to 240 in f1e5c94
if scale < 0 {
Err(ArrowError::ComputeError(
"Negative scale is not supported".into(),
))
} else if scale == 0 {

Update: this is fine, callers guard against passing in negative scale so this is intended

@Jefffrey

Thank you for double checknig @Jefffrey and for your help getting this resolved @shifluxxc

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Allow log/pow on negative scale decimals #19250

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	if scale < 0 {
	Err(ArrowError::ComputeError(
	"Negative scale is not supported".into(),
	))
	} else if scale == 0 {

Allow log/pow on negative scale decimals #19250

Description

Is your feature request related to a problem or challenge?

Describe the solution you'd like

Additional context

Activity

shifluxxc commented on Dec 13, 2025

shifluxxc commented on Dec 14, 2025

Jefffrey commented on Dec 19, 2025

shifluxxc commented on Dec 19, 2025

alamb commented on Dec 31, 2025

Jefffrey commented on Dec 31, 2025

alamb commented on Dec 31, 2025

shifluxxc commented on Dec 31, 2025

Jefffrey commented on Jan 6, 2026

alamb commented on Jan 7, 2026

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