Don't use is_infinite() where isinf() will do.

Places that aren't testing for sign should not use the more expensive
function; it's just wasteful, not to mention being a cognitive load
for readers who may know what isinf() is but not is_infinite().

As things stand, we actually don't need is_infinite() anyplace except
float4out/float8out, which means it could potentially go away altogether
after the changes I proposed in <13178.1538794717@sss.pgh.pa.us>.

src/backend/utils/adt/formatting.c

@@ -5731,7 +5731,7 @@ float4_to_char(PG_FUNCTION_ARGS)
 		numstr = orgnum = int_to_roman((int) rint(value));
 	else if (IS_EEEE(&Num))
 	{
-		if (isnan(value) || is_infinite(value))
+		if (isnan(value) || isinf(value))
 		{
 			/*
 			 * Allow 6 characters for the leading sign, the decimal point,
@@ -5835,7 +5835,7 @@ float8_to_char(PG_FUNCTION_ARGS)
 		numstr = orgnum = int_to_roman((int) rint(value));
 	else if (IS_EEEE(&Num))
 	{
-		if (isnan(value) || is_infinite(value))
+		if (isnan(value) || isinf(value))
 		{
 			/*
 			 * Allow 6 characters for the leading sign, the decimal point,

src/backend/utils/adt/rangetypes_selfuncs.c

@@ -17,6 +17,8 @@
  */
 #include "postgres.h"
 
+#include <math.h>
+
 #include "access/htup_details.h"
 #include "catalog/pg_operator.h"
 #include "catalog/pg_statistic.h"
@@ -750,19 +752,19 @@ get_position(TypeCacheEntry *typcache, RangeBound *value, RangeBound *hist1,
 static double
 get_len_position(double value, double hist1, double hist2)
 {
-	if (!is_infinite(hist1) && !is_infinite(hist2))
+	if (!isinf(hist1) && !isinf(hist2))
 	{
 		/*
 		 * Both bounds are finite. The value should be finite too, because it
 		 * lies somewhere between the bounds. If it doesn't, just return
 		 * something.
 		 */
-		if (is_infinite(value))
+		if (isinf(value))
 			return 0.5;
 
 		return 1.0 - (hist2 - value) / (hist2 - hist1);
 	}
-	else if (is_infinite(hist1) && !is_infinite(hist2))
+	else if (isinf(hist1) && !isinf(hist2))
 	{
 		/*
 		 * Lower bin boundary is -infinite, upper is finite. Return 1.0 to
@@ -770,7 +772,7 @@ get_len_position(double value, double hist1, double hist2)
 		 */
 		return 1.0;
 	}
-	else if (is_infinite(hist1) && is_infinite(hist2))
+	else if (isinf(hist1) && isinf(hist2))
 	{
 		/* same as above, but in reverse */
 		return 0.0;
@@ -851,7 +853,7 @@ calc_length_hist_frac(Datum *length_hist_values, int length_hist_nvalues,
 		return 0.0;				/* shouldn't happen, but doesn't hurt to check */
 
 	/* All lengths in the table are <= infinite. */
-	if (is_infinite(length2) && equal)
+	if (isinf(length2) && equal)
 		return 1.0;
 
 	/*----------
@@ -978,7 +980,7 @@ calc_length_hist_frac(Datum *length_hist_values, int length_hist_nvalues,
 	 * length2 is infinite. It's not clear what the correct value would be in
 	 * that case, so 0.5 seems as good as any value.
 	 */
-	if (is_infinite(area) && is_infinite(length2))
+	if (isinf(area) && isinf(length2))
 		frac = 0.5;
 	else
 		frac = area / (length2 - length1);