Fix behavior of Math.sqrt at 0 (#9818) (#9828)

* Fix behavior of Math.sqrt at 0 (#9818)

CHANGELOG_BEGIN
[Daml Compiler] Ensure that sqrt(0.0) == 0 and 0 ** 0 == 1
CHANGELOG_END

compiler/damlc/daml-stdlib-src/DA/Math.daml

@@ -25,7 +25,10 @@ infixr 8 **
 
 -- | Take a power of a number Example: `2.0 ** 3.0 == 8.0`.
 (**) : Decimal -> Decimal -> Decimal
-x ** y = exp (y * log x)
+x ** y
+  | y == 0.0 = 1.0
+  | x == 0.0 = 0.0
+  | otherwise = exp (y * log x)
 
 -- | Calculate the square root of a Decimal.
 --
@@ -34,7 +37,9 @@ x ** y = exp (y * log x)
 -- 1.2
 -- ```
 sqrt : Decimal -> Decimal
-sqrt x = x ** 0.5
+sqrt x
+  | x < 0.0 = error "sqrt is defined only for non-negative numbers"
+  | otherwise = x ** 0.5
 
 -- | The exponential function. Example: `exp 0.0 == 1.0`
 exp : Decimal -> Decimal
@@ -47,7 +52,9 @@ exp x
 
 -- | The natural logarithm. Example: `log 10.0 == 2.30258509299`
 log : Decimal -> Decimal
-log x = logt10k x / 10000.0
+log x
+  | x <= 0.0 = error "logarithm is defined only for positive numbers"
+  | otherwise = logt10k x / 10000.0
 
 -- | The logarithm of a number to a given base. Example: `log 10.0 100.0 == 2.0`
 logBase : Decimal -> Decimal -> Decimal

compiler/damlc/tests/daml-test-files/Math.daml

@@ -2,7 +2,7 @@
 -- All rights reserved.
 
 -- @INFO range=47:22-47:32; Use sqrt
--- @INFO range=57:15-57:25; Use sqrt
+-- @INFO range=66:15-66:25; Use sqrt
 
 
 module Math where
@@ -45,6 +45,15 @@ powerTest = scenario do
   let
     sqrt2 = 1.4142135623 : Decimal
   assert(abs(sqrt2 - 2.0 ** 0.5) <= 0.0000000001)
+  0.0 ** 0.0 === 1.0
+  0.0 ** 1.0 === 0.0
+  42.0 ** 0.0 === 1.0
+
+sqrtTest = scenario do
+  let
+    sqrt2 = 1.4142135623 : Decimal
+  assert(abs(sqrt2 - sqrt 2.0) <= 0.0000000001)
+  sqrt 0.0 === 0.0
 
 trigTest = scenario do
   let