From 226074e20648419c831d46971e3e630818ae063a Mon Sep 17 00:00:00 2001
From: Gil Forsyth <gil@forsyth.dev>
Date: Wed, 2 Nov 2022 12:43:43 -0400
Subject: [PATCH] feat: add support for ops.Log

if `base` isn't specified we default to the value of `e`
---
 ibis_substrait/compiler/mapping.py   |  1 +
 ibis_substrait/compiler/translate.py | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/ibis_substrait/compiler/mapping.py b/ibis_substrait/compiler/mapping.py
index af78e7ee..23d60079 100644
--- a/ibis_substrait/compiler/mapping.py
+++ b/ibis_substrait/compiler/mapping.py
@@ -32,6 +32,7 @@
     "Less": "lt",
     "LessEqual": "lte",
     "Ln": "ln",
+    "Log": "logb",
     "Log2": "log2",
     "Log10": "log10",
     "Lowercase": "lower",
diff --git a/ibis_substrait/compiler/translate.py b/ibis_substrait/compiler/translate.py
index a25c9d21..dd0d1c4a 100644
--- a/ibis_substrait/compiler/translate.py
+++ b/ibis_substrait/compiler/translate.py
@@ -11,10 +11,12 @@
 import decimal
 import functools
 import itertools
+import math
 import operator
 import uuid
 from typing import Any, Mapping, MutableMapping, Sequence, TypeVar
 
+import ibis
 import ibis.expr.datatypes as dt
 import ibis.expr.operations as ops
 import ibis.expr.schema as sch
@@ -1054,3 +1056,25 @@ def _extractdatefield(
     scalar_func.arguments.add(enum=stalg.FunctionArgument.Enum(specified=span))
     scalar_func.arguments.extend(arguments)
     return stalg.Expression(scalar_function=scalar_func)
+
+
+@translate.register(ops.Log)
+def _log(
+    op: ops.Log,
+    expr: ir.TableExpr,
+    compiler: SubstraitCompiler,
+    **kwargs: Any,
+) -> stalg.Expression:
+    arg = stalg.FunctionArgument(value=translate(op.arg, compiler, **kwargs))
+    base = stalg.FunctionArgument(
+        value=translate(
+            op.base if op.base is not None else ibis.literal(math.e), compiler, **kwargs
+        )
+    )
+
+    scalar_func = stalg.Expression.ScalarFunction(
+        function_reference=compiler.function_id(expr),
+        output_type=translate(expr.type()),
+        arguments=[arg, base],
+    )
+    return stalg.Expression(scalar_function=scalar_func)