From b002d95459ec9dbd439db8090694abdb885ad4a2 Mon Sep 17 00:00:00 2001
From: Rangi <remy.oukaour+rangi42@gmail.com>
Date: Wed, 27 Oct 2021 20:24:54 -0400
Subject: [PATCH] Fix precison of fixed-point formatting

Fixes #908
---
 src/asm/format.c                   | 20 ++++++--------------
 test/asm/fixed-point-precision.asm |  3 +++
 test/asm/fixed-point-precision.out |  5 +++--
 test/asm/string-formatting.out     |  2 +-
 4 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/src/asm/format.c b/src/asm/format.c
index 39b6a5b0..c4c7e947 100644
--- a/src/asm/format.c
+++ b/src/asm/format.c
@@ -228,21 +228,13 @@ void fmt_PrintNumber(char *buf, size_t bufLen, struct FormatSpec const *fmt, uin
 		/* Default fractional width (C's is 6 for "%f"; here 5 is enough) */
 		size_t fracWidth = fmt->hasFrac ? fmt->fracWidth : 5;
 
-		if (fracWidth) {
-			if (fracWidth > 255) {
-				error("Fractional width %zu too long, limiting to 255\n",
-				      fracWidth);
-				fracWidth = 255;
-			}
-
-			char spec[16]; /* Max "%" + 5-char PRIu32 + ".%0255.f" + terminator */
-
-			snprintf(spec, sizeof(spec), "%%" PRIu32 ".%%0%zu.f", fracWidth);
-			snprintf(valueBuf, sizeof(valueBuf), spec, value >> 16,
-				 (value % 65536) / 65536.0 * pow(10, fracWidth) + 0.5);
-		} else {
-			snprintf(valueBuf, sizeof(valueBuf), "%" PRIu32, value >> 16);
+		if (fracWidth > 255) {
+			error("Fractional width %zu too long, limiting to 255\n",
+			      fracWidth);
+			fracWidth = 255;
 		}
+
+		snprintf(valueBuf, sizeof(valueBuf), "%.*f", (int)fracWidth, value / 65536.0);
 	} else {
 		char const *spec = fmt->type == 'd' ? "%" PRId32
 				 : fmt->type == 'u' ? "%" PRIu32
diff --git a/test/asm/fixed-point-precision.asm b/test/asm/fixed-point-precision.asm
index 9ae79d83..84438ec2 100644
--- a/test/asm/fixed-point-precision.asm
+++ b/test/asm/fixed-point-precision.asm
@@ -9,3 +9,6 @@ pr = 16.12
 
 fl = 6.283185
 	println "`6.283185`: {.6f:fl} -> ${08x:fl}"
+
+fr = MUL(20.0, 0.32)
+	println "32% of 20 = {f:fr} (~{.2f:fr}) (~~{.0f:fr})"
diff --git a/test/asm/fixed-point-precision.out b/test/asm/fixed-point-precision.out
index ed6a3361..ad3b15e3 100644
--- a/test/asm/fixed-point-precision.out
+++ b/test/asm/fixed-point-precision.out
@@ -1,5 +1,6 @@
-`3.1`:    3.100007 -> $0003199a
+`3.1`:    3.100006 -> $0003199a
 `5.2`:    5.199997 -> $00053333
 `MUL`:   16.120026 -> $00101eba
-`16.12`: 16.119996 -> $00101eb8
+`16.12`: 16.119995 -> $00101eb8
 `6.283185`: 6.283188 -> $0006487f
+32% of 20 = 6.40015 (~6.40) (~~6)
diff --git a/test/asm/string-formatting.out b/test/asm/string-formatting.out
index 7072d1c5..a27663a9 100644
--- a/test/asm/string-formatting.out
+++ b/test/asm/string-formatting.out
@@ -1,5 +1,5 @@
 < 300  > <+00300> <  12c> <      %100101100>
 <4294967254> <-42> <&000037777777726>
-<3.14159> <-00123> <-123.0455932618>
+<3.14159> <-00123> <-123.0455932617>
 <hello     > <     hello>
 <300   >