[css-values-4] Fully sync the trig/pow functions with JS, wrt pos/neg 0. Fixes #4158.

Author: tabatkins

css-values-4/Overview.bs

@@ -2632,6 +2632,10 @@ Argument Ranges</h4>
 	the result is NaN.
 	(See [[#calc-type-checking]] for details on how [=math functions=] handle NaN.)
 
+	In ''sin(A)'' or ''tan(A)'',
+	if A is 0⁻,
+	the result is 0⁻.
+
 	In ''tan(A)'', if A is one of the asymptote values
 	(such as ''90deg'', ''270deg'', etc),
 	the result must be +∞ for ''90deg'' and all values a multiple of ''360deg'' from that
@@ -2650,22 +2654,78 @@ Argument Ranges</h4>
 	if A is less than -1 or greater than 1,
 	the result is NaN.
 
+	In ''acos(A)'',
+	if A is exactly 1,
+	the result is 0.
+
+	In ''asin(A)'' or ''atan(A)'',
+	if A is 0⁻,
+	the result is 0⁻.
+
 	In ''atan(A)'',
 	if A is +∞,
 	the result is ''90deg'';
 	if A is −∞,
 	the result is ''-90deg''.
 
-	In ''atan2(A, B)'',
-	if A and B are both zero,
-	the result is ''0deg''.
-	If either or both [=calculations=] are infinite,
-	the function must return an angle
-	as if the infinite value was replaced by ''1'' (for +∞) or ''-1'' (for −∞)
-	and the finite value was replaced by ''0'':
-	''atan2(finite, ∞)'' must return ''0deg'', as if it were ''atan2(0, 1)'';
-	''atan2(∞, ∞)'' must return ''45deg'', as if it were ''atan2(1, 1)'';
-	and so on around the circle.
+	In ''atan2(Y, X)'',
+	the following table gives the results for all unusual argument combinations:
+
+	<table class=data>
+		<thead>
+			<tr><td style="border:none" colspan=2><th colspan=6>X
+			<tr><td style="border:none" colspan=2><th>−∞ <th>-finite <th>0⁻ <th>0⁺ <th>+finite <th>+∞
+		</thead>
+		<tr>
+			<th rowspan=6 style="border-right:1px solid silver">Y
+			<th style="border-right: black 2px solid">−∞
+			<td>-135deg
+			<td>-90deg
+			<td>-90deg
+			<td>-90deg
+			<td>-90deg
+			<td>-45deg
+		<tr>
+			<th>-finite
+			<td>-180deg
+			<td>(normal)
+			<td>-90deg
+			<td>-90deg
+			<td>(normal)
+			<td>0⁻deg
+		<tr>
+			<th>0⁻
+			<td>-180deg
+			<td>-180deg
+			<td>-180deg
+			<td>0⁻deg
+			<td>0⁻deg
+			<td>0⁻deg
+		<tr>
+			<th>0⁺
+			<td>180deg
+			<td>180deg
+			<td>180deg
+			<td>0⁺deg
+			<td>0⁺deg
+			<td>0⁺deg
+		<tr>
+			<th>+finite
+			<td>180deg
+			<td>(normal)
+			<td>90deg
+			<td>90deg
+			<td>(normal)
+			<td>0⁺deg
+		<tr>
+			<th>+∞
+			<td>135deg
+			<td>90deg
+			<td>90deg
+			<td>90deg
+			<td>90deg
+			<td>45deg
+	</table>
 
 	Note: All of these behaviors are intended to match the "standard" definitions of these functions
 	as implemented by most programming languages,
@@ -2839,77 +2899,57 @@ Exponential  Functions: ''pow()'', ''sqrt()'', ''hypot()''</h3>
 Argument Ranges</h4>
 
 	In ''pow(A, B)'',
-	if A is negative,
+	if A is negative and finite,
+	and B is finite,
 	B must be an integer,
 	or else the result is NaN.
 
-	If A and B are both 0,
-	the result is 1.
-	If A is 0⁺ and B is negative,
-	the result is +∞;
-	if A is 0⁻ and B is negative,
-	the result is −∞.
-
-	If A or B is infinite,
+	If A or B are infinite or 0,
 	the following tables give the results:
 
-	<table class=data>
+	<table class=data style="table-layout:fixed">
 		<thead>
-			<tr><th scope=col colspan=3>A is +∞
-			<tr>
-				<th>B is < 0
-				<th>B is 0
-				<th>B is > 0
+			<tr><td>
+				<th>A is −∞
+				<th>A is 0⁻
+				<th>A is 0⁺
+				<th>A is +∞
 		</thead>
 		<tr>
-			<td>result is 0⁺
-			<td>result is 1
-			<td>result is +∞
-	</table>
-
-	<table class=data>
-		<thead>
-			<tr><th scope=col colspan=3>A is −∞
-			<tr>
-				<th>B is < 0
-				<th>B is 0
-				<th>B is > 0
-		</thead>
+			<th>B is −finite
+			<td>0⁻ if B is an odd integer, 0⁺ otherwise
+			<td>−∞ if B is an odd integer, +∞ otherwise
+			<td>+∞
+			<td>0⁺
 		<tr>
-			<td>result is 0⁻ if B is an odd integer, 0⁺ otherwise
-			<td>result is 1
-			<td>result is −∞ if B is an odd integer, +∞ otherwise
+			<th>B is 0
+			<td colspan=4>always 1
+		<tr>
+			<th>B is +finite
+			<td>−∞ if B is an odd integer, +∞ otherwise
+			<td>0⁻ if B is an odd integer, 0⁺ otherwise
+			<td>0⁺
+			<td>+∞
 	</table>
 
 	<table class=data>
 		<thead>
-			<tr><th scope=col colspan=5>B is +∞
-			<tr>
+			<tr><td>
 				<th>A is < -1
 				<th>A is -1
 				<th>-1 < A < 1
 				<th>A is 1
 				<th>A is > 1
 		</thead>
 		<tr>
+			<th>B is +∞
 			<td>result is +∞
 			<td>result is NaN
 			<td>result is 0⁺
 			<td>result is NaN
 			<td>result is +∞
-	</table>
-
-	<table class=data>
-		<thead>
-			<tr><th scope=col colspan=5>B is −∞
-			<tr>
-				<th>A is < -1
-				<th>A is -1
-				<th>-1 < A < 1
-				<th>A is 1
-				<th>A is > 1
-		</thead>
 		<tr>
+			<th>B is −∞
 			<td>result is 0⁺
 			<td>result is NaN
 			<td>result is +∞
@@ -2920,6 +2960,8 @@ Argument Ranges</h4>
 	In ''sqrt(A)'',
 	if A is +∞,
 	the result is +∞.
+	If A is 0⁻,
+	the result is 0⁻.
 	If A is less than 0,
 	the result is NaN.
 
@@ -2933,6 +2975,12 @@ Argument Ranges</h4>
 	as implemented by most programming languages,
 	in particular as implemented in JS.
 
+	Issue: Per JS, hypot(∞, NaN) yields ∞, and pow(NaN, 0) yields 1.
+	This violates the standard calculation rules of NaNs being fully infective.
+	Do we want to carry that behavior over as well?
+	Or maybe specifically undefine it,
+	since it's just error behavior?
+
 
 <h3 id='calc-syntax'>
 Syntax</h3>
@@ -3114,7 +3162,7 @@ Type Checking</h3>
 	and between nested calculations:
 
 	* Negative zero
-		(0<sup>−</sup>)
+		(0⁻)
 		can be produced literally by negating a zero
 		(''-0''),
 		or by a multiplication or division that produces zero
@@ -3131,41 +3179,41 @@ Type Checking</h3>
 		they're "censored" away into an "unsigned" zero.
 	* ''-0 + -0''
 		or ''-0 - 0''
-		produces 0<sup>−</sup>.
+		produces 0⁻.
 		All other additions or subtractions that would produce a zero
-		produce 0<sup>+</sup>.
-	* Multiplying or dividing 0<sup>−</sup> with a positive number
-		(including 0<sup>+</sup>)
+		produce 0⁺.
+	* Multiplying or dividing 0⁻ with a positive number
+		(including 0⁺)
 		produces a negative result
-		(either 0<sup>−</sup> or −∞),
-		while multiplying or dividing 0<sup>−</sup> with a negative number
+		(either 0⁻ or −∞),
+		while multiplying or dividing 0⁻ with a negative number
 		produces a positive result.
 
 		(In other words,
-		multiplying or dividing with 0<sup>−</sup>
+		multiplying or dividing with 0⁻
 		follows standard sign rules.)
-	* When comparing 0<sup>+</sup> and 0<sup>−</sup>,
-		0<sup>−</sup> is less than 0<sup>+</sup>.
-		For example, ''min(0, -0)'' must produce 0<sup>−</sup>,
-		''max(0, -0)'' must produce 0<sup>+</sup>,
-		and ''clamp(0, -0, 1)'' must produce 0<sup>+</sup>.
+	* When comparing 0⁺ and 0⁻,
+		0⁻ is less than 0⁺.
+		For example, ''min(0, -0)'' must produce 0⁻,
+		''max(0, -0)'' must produce 0⁺,
+		and ''clamp(0, -0, 1)'' must produce 0⁺.
 
 	If a <dfn export>top-level calculation</dfn>
 	(a [=math function=] not nested inside of another [=math function=])
 	would produce a NaN,
 	it instead produces +∞.
-	If a [=top-level calculation=] would produce 0<sup>−</sup>,
+	If a [=top-level calculation=] would produce 0⁻,
 	it instead produces the standard "unsigned" zero.
 
 	<div class=example>
 		For example, ''calc(-5 * 0)'' produces an unsigned zero--
-		the calculation resolves to 0<sup>−</sup>,
+		the calculation resolves to 0⁻,
 		but as it's a [=top-level calculation=],
 		it's then censored to an unsigned zero.
 
 		On the other hand, ''calc(1 / calc(-5 * 0))'' produces −∞,
 		same as ''calc(1 / (-5 * 0))''--
-		the inner calc resolves to 0<sup>−</sup>,
+		the inner calc resolves to 0⁻,
 		and as it's not a [=top-level calculation=],
 		it passes it up unchanged to the outer calc to produce −∞.
 		If it was censored into an unsigned zero,