otp: avoid pow() when displaying asset amounts
What the developer wrote
Authored by Jon Griffiths
otp: avoid pow() when displaying asset amounts
Removing this last use means we save 3924 bytes by removing the
floating point pow() implementation code.
What changed, and why it matters
This commit is a harmless code-size optimization. It replaces the mathematical pow() function (used to calculate 10 raised to a small power) with a simple lookup table of powers of 10, allowing the compiler to remove the floating-point pow() library code and save about 3.9 KB of firmware space. The displayed asset amounts are computed the same way as before.
No security action needed. Treat as a normal firmware size/optimization improvement.
Security signals we found
No strong security signals were identified.
Evidence from the diff
In main/ui/sign_tx.c, the code previously called pow(10, asset_info.precision) to obtain a uint32_t scale factor for formatting asset/fee amounts. The commit removes the
Changed components
main/ui/sign_tx.cInspect captured patch +10 / −3
diff --git a/main/ui/sign_tx.c b/main/ui/sign_tx.c
index 2a534bc..8e02dd6 100644
--- a/main/ui/sign_tx.c
+++ b/main/ui/sign_tx.c
@@ -1,7 +1,6 @@
#ifndef AMALGAMATED_BUILD
#include <assets_snapshot.h>
#include <inttypes.h>
-#include <math.h>
#include <wally_elements.h>
#include <wally_transaction.h>
@@ -30,6 +29,14 @@ static const char VERIFIED_WALLET_OUTPUT_MSG[] = "Verified wallet output";
static const char TICKER_BTC[] = "BTC";
+static const uint32_t POW_10[9] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000 };
+
+static uint32_t get_asset_scale_factor(const asset_info_t* asset_info)
+{
+ JADE_ASSERT(asset_info && asset_info->precision < sizeof(POW_10) / sizeof(POW_10[0]));
+ return POW_10[asset_info->precision];
+}
+
// Don't display pre-validated (eg. change) outputs (if provided) unless they have an associated warning message.
// Should work for elements and standard btc, but liquid hides scriptless outputs (fees)
static bool display_output(
@@ -115,7 +122,7 @@ static bool get_asset_display_info(const network_t network_id, const asset_info_
}
// Amount scaled and displayed at relevant precision
- const uint32_t scale_factor = pow(10, asset_info.precision);
+ const uint32_t scale_factor = get_asset_scale_factor(&asset_info);
ret = snprintf(amount, amount_len, "%.*f", asset_info.precision, 1.0 * value / scale_factor);
JADE_ASSERT(ret > 0 && ret < amount_len);
@@ -773,7 +780,7 @@ bool show_elements_final_confirmation_activity(
// Fee amount scaled and displayed at relevant precision
char feeamount[32];
- const uint32_t scale_factor = pow(10, asset_info.precision);
+ const uint32_t scale_factor = get_asset_scale_factor(&asset_info);
ret = snprintf(feeamount, sizeof(feeamount), "%.*f", asset_info.precision, 1.0 * fee / scale_factor);
JADE_ASSERT(ret > 0 && ret < sizeof(feeamount));
Why this scored 15/100
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