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common: extract fp16 routines into their own file.

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We might want to use them elsewhere.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2021-02-01 13:29:18 +10:30
parent 06a54606a3
commit cc4ea9420a
8 changed files with 82 additions and 54 deletions
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42
common/gossmap.c
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@@ -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;