Bug#1122073: satpy doesn't handle NaN appropriately on riscv64

[Paul Gevers]

Package: python3-satpy
Version: 0.59.0-1
Tags: patch

Hi,

As part of a request to help satpy to testing, it was discovered by 
Aurelien that satpy doesn't handle NaN properly and he provides a patch, 
see below.

Paul

-------- Forwarded Message --------
Subject: Re: Bug#1121879: release.debian.org: Help satpy migrate to testing
Date: Fri, 5 Dec 2025 19:57:31 +0100
From: Aurelien Jarno <aurel32 at debian.org>
To: Paul Gevers <elbrus at debian.org>
CC: Bas Couwenberg <sebastic at debian.org>, 1121879 at bugs.debian.org, 
debian-riscv at lists.debian.org

Hi,

On 2025-12-04 08:49, Paul Gevers wrote:
> user debian-riscv at lists.debian.org
> usertag riscv64
> thanks
> 
> Hi,
> 
> On 12/4/25 05:33, Bas Couwenberg wrote:
> > Please help satpy migrate to testing, the autopkgtest failures on riscv64 & s390x are not regressions, but are not detected as such.
> 
> 
> The package got removed from testing, so the package is considered new. For
> new packages, any failure is preventing migration. I'll ignore the s390x
> failure as that's a test dependency that can't be installed there
> (python3-satpy is arch:all and can be installed, but not all its
> Recommends). The riscv64 failure should be investigated as that seems to
> point out a genuine issue (which of course can be a bad test, but then
> fixing the test is the proper course of action). Adding riscv64 porters for
> that.

This is indeed a real issue. The conversion of a NaN to an int is 
undefined. It appears to be 0 on most CPUs, but it is not the case on 
riscv64.

The issue is actually already known upstream:
https://github.com/pytroll/satpy/issues/2934

The following patch fixes the issue on riscv64. It also removes the 
warning on other architectures.

--- satpy-0.59.0.orig/satpy/enhancements/colormap.py
+++ satpy-0.59.0/satpy/enhancements/colormap.py
@@ -41,9 +41,10 @@ def lookup(img, **kwargs):
  @on_separate_bands
  @using_map_blocks
  def _lookup_table(band_data, luts=None, index=-1):
-    # NaN/null values will become 0
      lut = luts[:, index] if len(luts.shape) == 2 else luts
-    band_data = band_data.clip(0, lut.size - 1).astype(np.uint8)
+    band_data = band_data.clip(0, lut.size - 1)
+    # Convert to uint8, with NaN/null values changed into 0
+    band_data = np.nan_to_num(band_data).astype(np.uint8)
      return lut[band_data]

Regards
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien at aurel32.net                     http://aurel32.net

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