util: Add PruneMiBtoGB() function

Now the text of prune QCheckBox shows the space in GB instead of
thousands MiB, which is consistent with other parts of the GUI.

Author: hebasto

src/qt/intro.cpp

@@ -12,6 +12,7 @@
 
 #include <qt/guiconstants.h>
 #include <qt/guiutil.h>
+#include <qt/optionsmodel.h>
 
 #include <interfaces/node.h>
 #include <util/system.h>
@@ -23,7 +24,7 @@
 #include <cmath>
 
 /* Total required space (in GB) depending on user choice (prune, not prune) */
-static uint64_t requiredSpace;
+static int64_t requiredSpace;
 
 /* Check free space asynchronously to prevent hanging the UI thread.
 
@@ -130,18 +131,18 @@ Intro::Intro(QWidget *parent, uint64_t blockchain_size, uint64_t chain_state_siz
     );
     ui->lblExplanation2->setText(ui->lblExplanation2->text().arg(PACKAGE_NAME));
 
-    uint64_t pruneTarget = std::max<int64_t>(0, gArgs.GetArg("-prune", 0));
-    if (pruneTarget > 1) { // -prune=1 means enabled, above that it's a size in MB
+    int64_t prune_target_mib = std::max<int64_t>(0, gArgs.GetArg("-prune", 0));
+    if (prune_target_mib > 1) { // -prune=1 means enabled, above that it's a size in MiB
         ui->prune->setChecked(true);
         ui->prune->setEnabled(false);
     }
-    ui->prune->setText(tr("Discard blocks after verification, except most recent %1 GB (prune)").arg(pruneTarget ? pruneTarget / 1000 : DEFAULT_PRUNE_TARGET_GB));
+    const int prune_target_gb = PruneMiBtoGB(prune_target_mib);
+    ui->prune->setText(tr("Discard blocks after verification, except most recent %1 GB (prune)").arg(prune_target_gb ? prune_target_gb : DEFAULT_PRUNE_TARGET_GB));
     requiredSpace = m_blockchain_size;
     QString storageRequiresMsg = tr("At least %1 GB of data will be stored in this directory, and it will grow over time.");
-    if (pruneTarget) {
-        uint64_t prunedGBs = std::ceil(pruneTarget * 1024 * 1024.0 / GB_BYTES);
-        if (prunedGBs <= requiredSpace) {
-            requiredSpace = prunedGBs;
+    if (prune_target_gb) {
+        if (prune_target_gb <= requiredSpace) {
+            requiredSpace = prune_target_gb;
             storageRequiresMsg = tr("Approximately %1 GB of data will be stored in this directory.");
         }
         ui->lblExplanation3->setVisible(true);

src/qt/optionsmodel.h

@@ -6,6 +6,7 @@
 #define BITCOIN_QT_OPTIONSMODEL_H
 
 #include <amount.h>
+#include <qt/guiconstants.h>
 
 #include <QAbstractListModel>
 
@@ -16,6 +17,11 @@ class Node;
 extern const char *DEFAULT_GUI_PROXY_HOST;
 static constexpr unsigned short DEFAULT_GUI_PROXY_PORT = 9050;
 
+/**
+ * Convert configured prune target MiB to displayed GB. Round up to avoid underestimating max disk usage.
+ */
+static inline int PruneMiBtoGB(int64_t mib) { return (mib * 1024 * 1024 + GB_BYTES - 1) / GB_BYTES; }
+
 /** Interface from Qt to configuration data structure for Bitcoin client.
    To Qt, the options are presented as a list with the different options
    laid out vertically.