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| author | Andrew Chow <achow101-github@achow101.com> | 2021-09-10 20:24:44 -0400 |
|---|---|---|
| committer | Andrew Chow <achow101-github@achow101.com> | 2021-10-08 13:53:48 -0400 |
| commit | 0fbaef9676a1dcb84bcf95afd8d994831ab327b6 (patch) | |
| tree | 4d41871f8100e99b7412983e5e7f028d15f6ecf8 /src/policy | |
| parent | 927586990eb9bc8403a3831247847bdd3bf60423 (diff) | |
| download | bitcoin-0fbaef9676a1dcb84bcf95afd8d994831ab327b6.tar.xz | |
fees: Always round up fee calculated from a feerate
When calculating the fee for a given tx size from a fee rate, we should
always round up to the next satoshi. Otherwise, if we round down (via
truncation), the calculated fee may result in a fee with a feerate
slightly less than targeted.
This is particularly important for coin selection as a slightly lower
feerate than expected can result in a variety of issues.
Diffstat (limited to 'src/policy')
| -rw-r--r-- | src/policy/feerate.cpp | 6 | ||||
| -rw-r--r-- | src/policy/feerate.h | 1 |
2 files changed, 6 insertions, 1 deletions
diff --git a/src/policy/feerate.cpp b/src/policy/feerate.cpp index 25b9282b4e..ce149067b7 100644 --- a/src/policy/feerate.cpp +++ b/src/policy/feerate.cpp @@ -7,6 +7,8 @@ #include <tinyformat.h> +#include <cmath> + CFeeRate::CFeeRate(const CAmount& nFeePaid, uint32_t num_bytes) { const int64_t nSize{num_bytes}; @@ -22,7 +24,9 @@ CAmount CFeeRate::GetFee(uint32_t num_bytes) const { const int64_t nSize{num_bytes}; - CAmount nFee = nSatoshisPerK * nSize / 1000; + // Be explicit that we're converting from a double to int64_t (CAmount) here. + // We've previously had issues with the silent double->int64_t conversion. + CAmount nFee{static_cast<CAmount>(std::ceil(nSatoshisPerK * nSize / 1000.0))}; if (nFee == 0 && nSize != 0) { if (nSatoshisPerK > 0) nFee = CAmount(1); diff --git a/src/policy/feerate.h b/src/policy/feerate.h index b16f3f8251..8ba896bb01 100644 --- a/src/policy/feerate.h +++ b/src/policy/feerate.h @@ -48,6 +48,7 @@ public: CFeeRate(const CAmount& nFeePaid, uint32_t num_bytes); /** * Return the fee in satoshis for the given size in bytes. + * If the calculated fee would have fractional satoshis, then the returned fee will always be rounded up to the nearest satoshi. */ CAmount GetFee(uint32_t num_bytes) const; /** |