From 181b7fe7e4d6b6685c99cb3811e0014b3f316ee6 Mon Sep 17 00:00:00 2001
From: Alex Shinn <alexshinn@gmail.com>
Date: Thu, 19 Nov 2020 13:13:37 +0900
Subject: [PATCH] preserve exactness in sqrt of ratios where possible

---
 eval.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/eval.c b/eval.c
index fc6e4818..1d44ea22 100644
--- a/eval.c
+++ b/eval.c
@@ -1662,8 +1662,10 @@ sexp sexp_exact_sqrt (sexp ctx, sexp self, sexp_sint_t n, sexp z) {
 #endif
 
 sexp sexp_sqrt (sexp ctx, sexp self, sexp_sint_t n, sexp z) {
-#if SEXP_USE_BIGNUMS
+#if SEXP_USE_BIGNUMS || SEXP_USE_RATIOS
   sexp_gc_var2(res, rem);
+#endif
+#if SEXP_USE_BIGNUMS
   if (sexp_bignump(z)) {
     sexp_gc_preserve2(ctx, res, rem);
     res = sexp_bignum_sqrt(ctx, z, &rem);
@@ -1673,6 +1675,20 @@ sexp sexp_sqrt (sexp ctx, sexp self, sexp_sint_t n, sexp z) {
     sexp_gc_release2(ctx);
     return res;
   }
+#endif
+#if SEXP_USE_RATIOS
+  if (sexp_ratiop(z)) {
+    sexp_gc_preserve2(ctx, res, rem);
+    res = sexp_sqrt(ctx, self, n, sexp_ratio_numerator(z));
+    rem = sexp_sqrt(ctx, self, n, sexp_ratio_denominator(z));
+    if (sexp_exactp(res) && sexp_exactp(rem)) {
+      res = sexp_make_ratio(ctx, res, rem);
+    } else {
+      res = sexp_inexact_sqrt(ctx, self, n, z);
+    }
+    sexp_gc_release2(ctx);
+    return res;
+  }
 #endif
   return sexp_inexact_sqrt(ctx, self, n, z);
 }