>From 6c39851e1504d01b2de05e014f5542913e3e5c5e Mon Sep 17 00:00:00 2001
From: Peter Bex <address@hidden>
Date: Sat, 17 Sep 2011 17:41:58 +0200
Subject: [PATCH] Do not drop precision in flonums when compiling

---
 c-backend.scm            |    2 ++
 tests/compiler-tests.scm |   13 +++++++++++++
 2 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/c-backend.scm b/c-backend.scm
index 1571edb..5dbcadd 100644
--- a/c-backend.scm
+++ b/c-backend.scm
@@ -60,6 +60,8 @@
 ;;; Generate target code:
 
 (define (generate-code literals lliterals lambdas out source-file dynamic db)
+  ;; Don't truncate floating-point precision!
+  (flonum-print-precision (+ flonum-maximum-decimal-exponent 1))
   (let ()
 
     ;; Some helper procedures
diff --git a/tests/compiler-tests.scm b/tests/compiler-tests.scm
index 7395130..226c440 100644
--- a/tests/compiler-tests.scm
+++ b/tests/compiler-tests.scm
@@ -216,3 +216,16 @@
     (assert (zero? b))))
 
 (gp-test)
+
+;; Test that encode-literal doesn't drop digits for extreme flonum values.
+
+;; This number is 2^971 * (2^53 - 1), and is the positive "all ones" number for
+;; 64-bit flonums with precision 53 and significand/mantissa 10.
+;; If we want to support 32-bit flonums or flonums with different precision
+;; or significand, we need a cond-expand here or something.
+;; Technically, even larger decimal numbers can be represented by flonums.
+;; This number can correctly be compared exactly.
+(assert (= (* (- (expt 2 flonum-precision) 1)
+              (expt 2 (- flonum-maximum-exponent flonum-precision)))
+           179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.0
+           (string->number "179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.0")))
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-- 
1.7.3.4