[libxslt] Handle negative xsl:number values

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 69ec3da1b653024aca6515ddd4adc91919dd188e
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sun Apr 10 12:51:57 2016 +0200

    Handle negative xsl:number values
    
    According to XSLT 2.0, negative values are a non-recoverable dynamic error.
    Print an error message and treat negative values as zero.
    
    Fixes an OOB array access in xsltNumberFormatAlpha.

 libxslt/numbers.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)
---
diff --git a/libxslt/numbers.c b/libxslt/numbers.c
index eb087bc..a3cabcf 100644
--- a/libxslt/numbers.c
+++ b/libxslt/numbers.c
@@ -246,7 +246,7 @@ xsltNumberFormatAlpha(xmlBufferPtr buffer,
        number--;
        *(--pointer) = alpha_list[((int)fmod(number, alpha_size))];
        number /= alpha_size;
-       if (fabs(number) < 1.0)
+       if (number < 1.0)
            break; /* for */
     }
     xmlBufferCCat(buffer, pointer);
@@ -442,6 +442,21 @@ xsltNumberFormatInsertNumbers(xsltNumberDataPtr data,
        number = numbers[(numbers_max - 1) - i];
         /* Round to nearest like XSLT 2.0 */
         number = floor(number + 0.5);
+        /*
+         * XSLT 1.0 isn't clear on how to handle negative numbers, but XSLT
+         * 2.0 says:
+         *
+         *     It is a non-recoverable dynamic error if any undiscarded item
+         *     in the atomized sequence supplied as the value of the value
+         *     attribute of xsl:number cannot be converted to an integer, or
+         *     if the resulting integer is less than 0 (zero).
+         */
+        if (number < 0.0) {
+            xsltTransformError(NULL, NULL, NULL,
+                    "xsl-number : negative value\n");
+            /* Recover by treating negative values as zero. */
+            number = 0.0;
+        }
        if (i < tokens->nTokens) {
          /*
           * The "n"th format token will be used to format the "n"th