From 35cca73d2fe67a8ca2914fa56d428b570aff3189 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 21 Mar 2022 11:28:28 +1030
Subject: [PATCH] devtools/fp16: conversion tool for fp16 format.

We use this in gossmap to represent htlc max/min approximations.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 devtools/Makefile |  4 +++-
 devtools/fp16.c   | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 devtools/fp16.c

diff --git a/devtools/Makefile b/devtools/Makefile
index 90dd7c7b4..181c1eae5 100644
--- a/devtools/Makefile
+++ b/devtools/Makefile
@@ -1,4 +1,4 @@
-DEVTOOLS := devtools/bolt11-cli devtools/decodemsg devtools/onion devtools/dump-gossipstore devtools/gossipwith devtools/create-gossipstore devtools/mkcommit devtools/mkfunding devtools/mkclose devtools/mkgossip devtools/mkencoded devtools/mkquery devtools/lightning-checkmessage devtools/topology devtools/route devtools/blindedpath devtools/bolt12-cli devtools/encodeaddr devtools/features
+DEVTOOLS := devtools/bolt11-cli devtools/decodemsg devtools/onion devtools/dump-gossipstore devtools/gossipwith devtools/create-gossipstore devtools/mkcommit devtools/mkfunding devtools/mkclose devtools/mkgossip devtools/mkencoded devtools/mkquery devtools/lightning-checkmessage devtools/topology devtools/route devtools/blindedpath devtools/bolt12-cli devtools/encodeaddr devtools/features devtools/fp16
 ifeq ($(HAVE_SQLITE3),1)
 DEVTOOLS += devtools/checkchannels
 endif
@@ -49,6 +49,8 @@ DEVTOOLS_COMMON_OBJS :=				\
 
 devtools/features: $(CCAN_OBJS) common/features.o common/utils.o wire/fromwire.o wire/towire.o devtools/features.o
 
+devtools/fp16: $(CCAN_OBJS) common/fp16.o common/utils.o common/setup.o common/autodata.o devtools/fp16.o
+
 devtools/bolt11-cli: $(DEVTOOLS_COMMON_OBJS) $(JSMN_OBJS) $(CCAN_OBJS) $(BITCOIN_OBJS) wire/fromwire.o wire/towire.o devtools/bolt11-cli.o
 
 devtools/encodeaddr: common/utils.o common/bech32.o devtools/encodeaddr.o
diff --git a/devtools/fp16.c b/devtools/fp16.c
new file mode 100644
index 000000000..4f541e863
--- /dev/null
+++ b/devtools/fp16.c
@@ -0,0 +1,45 @@
+/* Simple tool to convert to/from our internal fp16 representation */
+#include "config.h"
+#include <ccan/err/err.h>
+#include <ccan/opt/opt.h>
+#include <common/fp16.h>
+#include <common/setup.h>
+#include <common/type_to_string.h>
+#include <inttypes.h>
+#include <stdio.h>
+
+int main(int argc, char *argv[])
+{
+	fp16_t fp16val;
+	u64 u64min, u64max;
+	char *endp;
+
+	common_setup(argv[0]);
+
+	opt_register_noarg("-h|--help", opt_usage_and_exit,
+			   "[fp16:val|value]\n"
+			   "Converts to/from fp16, indicates ranges",
+			   "Get usage information");
+	opt_parse(&argc, argv, opt_log_stderr_exit);
+	if (argc != 2)
+		opt_usage_exit_fail("Expect 1 argument");
+
+	if (strstarts(argv[1], "fp16:"))
+		fp16val = strtoul(argv[1] + 5, &endp, 0);
+	else
+		fp16val = u64_to_fp16(strtoul(argv[1], &endp, 0), false);
+
+	if (*endp)
+		opt_usage_exit_fail("Expect valid number");
+
+	u64min = u64max = fp16_to_u64(fp16val);
+	while (u64_to_fp16(u64min-1, false) == fp16val)
+		u64min--;
+	while (u64_to_fp16(u64max+1, false) == fp16val)
+		u64max++;
+	printf("fp16:0x%x\n"
+	       "min %"PRIu64"\n"
+	       "max %"PRIu64"\n",
+	       fp16val, u64min, u64max);
+	common_shutdown();
+}