From 2da50875eed5a9043f080902fa4e0cd31d2bbc0c Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Fri, 14 Jun 2019 18:32:45 -0700
Subject: [PATCH] lib: setNaturalPrecisionUpTo

---
 hledger-lib/Hledger/Data/Amount.hs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hledger-lib/Hledger/Data/Amount.hs b/hledger-lib/Hledger/Data/Amount.hs
index 33543a1fc..79f503127 100644
--- a/hledger-lib/Hledger/Data/Amount.hs
+++ b/hledger-lib/Hledger/Data/Amount.hs
@@ -77,6 +77,7 @@ module Hledger.Data.Amount (
   withPrecision,
   setFullPrecision,
   setNaturalPrecision,
+  setNaturalPrecisionUpTo,
   setAmountInternalPrecision,
   withInternalPrecision,
   setAmountDecimalPoint,
@@ -298,6 +299,14 @@ setNaturalPrecision a = setAmountPrecision normalprecision a
   where
     normalprecision  = fromIntegral $ decimalPlaces $ normalizeDecimal $ aquantity a
 
+-- | Set an amount's display precision to just enough so that all
+-- significant decimal digits will be shown, but not more than the
+-- given maximum number of decimal digits.
+setNaturalPrecisionUpTo :: Int -> Amount -> Amount
+setNaturalPrecisionUpTo n a = setAmountPrecision (min n normalprecision) a
+  where
+    normalprecision  = fromIntegral $ decimalPlaces $ normalizeDecimal $ aquantity a
+
 -- | Get a string representation of an amount for debugging,
 -- appropriate to the current debug level. 9 shows maximum detail.
 showAmountDebug :: Amount -> String