common: extract fp16 routines into their own file.

We might want to use them elsewhere.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/Makefile

@@ -32,6 +32,7 @@ COMMON_SRC_NOGEN :=				\
 	common/ecdh_hsmd.c			\
 	common/features.c			\
 	common/fee_states.c			\
+	common/fp16.c				\
 	common/gossip_rcvd_filter.c		\
 	common/gossip_store.c			\
 	common/hash_u5.c			\

common/fp16.c

@@ -0,0 +1,50 @@
+#include "config.h"
+#include <assert.h>
+#include <ccan/bitops/bitops.h>
+#include <common/fp16.h>
+
+fp16_t u64_to_fp16(u64 val, bool round_up)
+{
+	u16 mantissa_bits, mantissa, exponent;
+
+	if (val == 0)
+		return 0;
+
+	/* How many bits do we need to represent mantissa? */
+	mantissa_bits = bitops_hs64(val) + 1;
+
+	/* We only have 11 bits, so if we need more, we will round. */
+	if (mantissa_bits > 11) {
+		exponent = mantissa_bits - 11;
+		mantissa = (val >> exponent);
+		/* If we're losing bits here, we're rounding down */
+		if (round_up && (val & ((1ULL << exponent)-1))) {
+			mantissa++;
+			if (mantissa == (1 << 11)) {
+				mantissa >>= 1;
+				exponent++;
+			}
+		}
+		/* huge number? Make it max. */
+		if (exponent >= 32) {
+			exponent = 31;
+			mantissa = (1 << 11)-1;
+		}
+	} else {
+		exponent = 0;
+		mantissa = val;
+	}
+
+	assert((mantissa >> 11) == 0);
+	return (exponent << 11) | mantissa;
+}
+
+bool amount_msat_less_fp16(struct amount_msat amt, fp16_t fp)
+{
+	return amt.millisatoshis < fp16_to_u64(fp); /* Raw: fp16 compare */
+}
+
+bool amount_msat_greater_fp16(struct amount_msat amt, fp16_t fp)
+{
+	return amt.millisatoshis > fp16_to_u64(fp); /* Raw: fp16 compare */
+}

common/fp16.h

@@ -0,0 +1,19 @@
+/* 5 bit exponent, 11 bit mantissa approximations of min/max */
+#ifndef LIGHTNING_COMMON_FP16_H
+#define LIGHTNING_COMMON_FP16_H
+#include "config.h"
+#include <common/amount.h>
+
+typedef u16 fp16_t;
+
+static inline u64 fp16_to_u64(fp16_t val)
+{
+	return ((u64)val & ((1 << 11)-1)) << (val >> 11);
+}
+
+fp16_t u64_to_fp16(u64 val, bool round_up);
+
+bool amount_msat_less_fp16(struct amount_msat amt, fp16_t fp);
+bool amount_msat_greater_fp16(struct amount_msat amt, fp16_t fp);
+
+#endif /* LIGHTNING_COMMON_FP16_H */

common/gossmap.c

@@ -227,42 +227,6 @@ struct gossmap_chan *gossmap_find_chan(const struct gossmap *map,
 	return NULL;
 }
 
-static fp16_t u64_to_fp16(u64 val, bool round_up)
-{
-	u16 mantissa_bits, mantissa, exponent;
-
-	if (val == 0)
-		return 0;
-
-	/* How many bits do we need to represent mantissa? */
-	mantissa_bits = bitops_hs64(val) + 1;
-
-	/* We only have 11 bits, so if we need more, we will round. */
-	if (mantissa_bits > 11) {
-		exponent = mantissa_bits - 11;
-		mantissa = (val >> exponent);
-		/* If we're losing bits here, we're rounding down */
-		if (round_up && (val & ((1ULL << exponent)-1))) {
-			mantissa++;
-			if (mantissa == (1 << 11)) {
-				mantissa >>= 1;
-				exponent++;
-			}
-		}
-		/* huge number? Make it max. */
-		if (exponent >= 32) {
-			exponent = 31;
-			mantissa = (1 << 11)-1;
-		}
-	} else {
-		exponent = 0;
-		mantissa = val;
-	}
-
-	assert((mantissa >> 11) == 0);
-	return (exponent << 11) | mantissa;
-}
-
 static u32 init_node_arr(struct gossmap_node *node_arr, size_t start)
 {
 	size_t i;
@@ -822,12 +786,10 @@ bool gossmap_chan_capacity(const struct gossmap_chan *chan,
 			   int direction,
 			   struct amount_msat amount)
 {
-	if (amount.millisatoshis /* Raw: fp16 compare */
-	    < fp16_to_u64(chan->half[direction].htlc_min))
+	if (amount_msat_less_fp16(amount, chan->half[direction].htlc_min))
 		return false;
 
-	if (amount.millisatoshis /* Raw: fp16 compare */
-	    > fp16_to_u64(chan->half[direction].htlc_max))
+	if (amount_msat_greater_fp16(amount, chan->half[direction].htlc_max))
 		return false;
 
 	return true;

common/gossmap.h

@@ -4,13 +4,11 @@
 #include <bitcoin/short_channel_id.h>
 #include <ccan/typesafe_cb/typesafe_cb.h>
 #include <common/amount.h>
+#include <common/fp16.h>
 
 struct node_id;
 struct pubkey32;
 
-/* 5 bit exponent, 11 bit mantissa approximations of min/max */
-typedef u16 fp16_t;
-
 struct gossmap_node {
 	/* Offset in memory map for node_announce, or 0. */
 	u32 nann_off;
@@ -38,11 +36,6 @@ struct gossmap_chan {
 	} half[2];
 };
 
-static inline u64 fp16_to_u64(fp16_t val)
-{
-	return ((u64)val & ((1 << 11)-1)) << (val >> 11);
-}
-
 struct gossmap *gossmap_load(const tal_t *ctx, const char *filename);
 
 /* Call this before using to ensure it's up-to-date.  Returns true if something

common/test/run-gossmap-fp16.c

@@ -1,5 +1,8 @@
+#include "../fp16.c"
+#include <common/pseudorand.h>
+#include <common/type_to_string.h>
 #include <stdio.h>
-#include "../gossmap.c"
+#include <wire/wire.h>
 
 /* AUTOGENERATED MOCKS START */
 /* Generated stub for amount_asset_is_main */