From b7a1201b72bf9d3c5288b4da9a920f32c4772230 Mon Sep 17 00:00:00 2001
From: itchyny <itchyny@cybozu.co.jp>
Date: Tue, 4 Mar 2025 22:09:33 +0900
Subject: [PATCH] Preserve numerical precision on `length/0` (#3275)

---
 src/builtin.c |  2 +-
 src/jv.c      | 15 +++++++++++++++
 src/jv.h      |  1 +
 tests/jq.test | 14 +++++++++++++-
 4 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/builtin.c b/src/builtin.c
index 79d1e896..06cd213d 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -497,7 +497,7 @@ static jv f_length(jq_state *jq, jv input) {
   } else if (jv_get_kind(input) == JV_KIND_STRING) {
     return jv_number(jv_string_length_codepoints(input));
   } else if (jv_get_kind(input) == JV_KIND_NUMBER) {
-    jv r = jv_number(fabs(jv_number_value(input)));
+    jv r = jv_number_abs(input);
     jv_free(input);
     return r;
   } else if (jv_get_kind(input) == JV_KIND_NULL) {
diff --git a/src/jv.c b/src/jv.c
index 4e50c582..3e9920ed 100644
--- a/src/jv.c
+++ b/src/jv.c
@@ -732,6 +732,21 @@ int jvp_number_is_nan(jv n) {
   return isnan(n.u.number);
 }
 
+jv jv_number_abs(jv n) {
+  assert(JVP_HAS_KIND(n, JV_KIND_NUMBER));
+
+#ifdef USE_DECNUM
+  if (JVP_HAS_FLAGS(n, JVP_FLAGS_NUMBER_LITERAL)) {
+    jvp_literal_number* m = jvp_literal_number_alloc(jvp_dec_number_ptr(n)->digits);
+
+    decNumberAbs(&m->num_decimal, jvp_dec_number_ptr(n), DEC_CONTEXT());
+    jv r = {JVP_FLAGS_NUMBER_LITERAL, 0, 0, 0, {&m->refcnt}};
+    return r;
+  }
+#endif
+  return jv_number(fabs(jv_number_value(n)));
+}
+
 jv jv_number_negate(jv n) {
   assert(JVP_HAS_KIND(n, JV_KIND_NUMBER));
 
diff --git a/src/jv.h b/src/jv.h
index 5c3b7c54..5d4197cf 100644
--- a/src/jv.h
+++ b/src/jv.h
@@ -74,6 +74,7 @@ jv jv_number(double);
 jv jv_number_with_literal(const char*);
 double jv_number_value(jv);
 int jv_is_integer(jv);
+jv jv_number_abs(jv);
 jv jv_number_negate(jv);
 
 int jv_number_has_literal(jv);
diff --git a/tests/jq.test b/tests/jq.test
index d5eb8dde..959895c4 100644
--- a/tests/jq.test
+++ b/tests/jq.test
@@ -2033,7 +2033,11 @@ map(abs)
 [-0, 0, -10, -1.1]
 [0,0,10,1.1]
 
-map(fabs == length) | unique
+map(fabs)
+[-0, 0, -10, -1.1]
+[0,0,10,1.1]
+
+map(abs == length) | unique
 [-10, -1.1, -1e-1, 1000000000000000002]
 [true]
 
@@ -2042,6 +2046,14 @@ map(abs)
 [0.1,1000000000000000002]
 [1e-1, 1000000000000000002]
 
+[1E+1000,-1E+1000 | abs | tojson] | unique == if have_decnum then ["1E+1000"] else ["1.7976931348623157e+308"] end
+null
+true
+
+[1E+1000,-1E+1000 | length | tojson] | unique == if have_decnum then ["1E+1000"] else ["1.7976931348623157e+308"] end
+null
+true
+
 # Using a keyword as variable/label name
 
 123 as $label | $label