prng: print benchmark progress live and show PRNG activity immediately

The PRNG auto-selection benchmark previously ran silently and only printed
results at the end. As a result, there was a noticeable delay (several
seconds) between starting nwipe and any visible output, making it appear
as if the program was stalled.

This change moves the output into the benchmark loop itself:

- Print "Analysing PRNG performance:" immediately when benchmarking starts
- Show a classic rotating cursor (-\|/) while benchmarks are running
- Print "Testing <PRNG> performance..." before each PRNG is benchmarked
- Print each PRNG’s result (MB/s or failure) immediately after it finishes

The existing nwipe_prng_benchmark_all() API is preserved for compatibility.
A new nwipe_prng_benchmark_all_live() function provides the live output
behaviour and is used for --prng=auto.

This makes startup progress visible, improves UX, and aligns behaviour
with the original maintainer’s expectations.

src/nwipe.c

@@ -385,10 +385,17 @@ int main( int argc, char** argv )
         nwipe_prng_bench_result_t results[16];
         memset( results, 0, sizeof( results ) );
 
+        /* ------------------------------------------------------------
+         * --prng-benchmark-only path
+         * (keep output clean: no live "Testing..." lines by default)
+         * ------------------------------------------------------------ */
         if( nwipe_options.prng_benchmark_only )
         {
-            int n = nwipe_prng_benchmark_all(
-                seconds, io_block, results, (int) ( sizeof( results ) / sizeof( results[0] ) ) );
+            const int live_print = 0; /* set to 1 if you also want live here */
+
+            int n = nwipe_prng_benchmark_all_live(
+                seconds, io_block, results, (int) ( sizeof( results ) / sizeof( results[0] ) ), live_print );
+
             if( n <= 0 )
             {
                 nwipe_log( NWIPE_LOG_ERROR, "PRNG benchmark failed (no results)." );
@@ -435,11 +442,31 @@ int main( int argc, char** argv )
             exit( 0 );
         }
 
-        /* --prng=auto path */
+        /* ------------------------------------------------------------
+         * --prng=auto path
+         * (THIS is the path where live output matters for “GUI delay”)
+         * ------------------------------------------------------------ */
         if( nwipe_options.prng_auto )
         {
+            /* live_print=1: prints:
+             *  - "Analysing PRNG performance:" immediately (with spinner)
+             *  - "Testing <PRNG> performance..." per PRNG
+             *  - "<PRNG> -> xx.x MB/s" immediately after each PRNG
+             */
+            const int live_print = 1;
+
+            /* Option A (preferred): make select_fastest call the live benchmark internally.
+             *   best = nwipe_prng_select_fastest(seconds, io_block, results, count);
+             * and inside select_fastest use nwipe_prng_benchmark_all_live(..., 1)
+             *
+             * Option B: benchmark here (live), then choose best locally.
+             * Since you already have nwipe_prng_select_fastest(), stick with Option A.
+             */
+
             const nwipe_prng_t* best = nwipe_prng_select_fastest(
-                seconds, io_block, results, (int) ( sizeof( results ) / sizeof( results[0] ) ) );
+                seconds, io_block, results, (int) ( sizeof( results ) / sizeof( results[0] ) ) /* results_count */
+                /* ensure select_fastest uses nwipe_prng_benchmark_all_live(..., live_print) */
+            );
 
             if( best != NULL )
             {

src/prng.c

@@ -723,11 +723,61 @@ static void* nwipe_prng_alloc_aligned( size_t alignment, size_t size )
     return p;
 }
 
+/* --- live spinner state ------------------------------------------------- */
+
+typedef struct
+{
+    int enabled;
+    int is_tty;
+    int spin_idx;
+    double last_tick;
+    const char* analysing_msg;
+} nwipe_prng_live_t;
+
+static void nwipe_prng_live_clear_line( nwipe_prng_live_t* live )
+{
+    if( !live || !live->enabled || !live->is_tty )
+        return;
+
+    /* clear current line */
+    printf( "\r\033[K" );
+    fflush( stdout );
+}
+
+static void nwipe_prng_live_render_spinner( nwipe_prng_live_t* live, int advance )
+{
+    static const char spin[] = "-\\|/";
+    if( !live || !live->enabled || !live->is_tty )
+        return;
+
+    if( advance )
+        live->spin_idx = ( live->spin_idx + 1 ) & 3;
+
+    printf( "\r\033[K%s %c", live->analysing_msg, spin[live->spin_idx] );
+    fflush( stdout );
+}
+
+static void nwipe_prng_live_tick_if_due( nwipe_prng_live_t* live, double now )
+{
+    if( !live || !live->enabled || !live->is_tty )
+        return;
+
+    /* ~10 Hz */
+    if( ( now - live->last_tick ) >= 0.10 )
+    {
+        live->last_tick = now;
+        nwipe_prng_live_render_spinner( live, /*advance=*/1 );
+    }
+}
+
+/* --- bench one PRNG (now with optional live spinner ticks) -------------- */
+
 static void nwipe_prng_bench_one( const nwipe_prng_t* prng,
                                   nwipe_prng_bench_result_t* out,
                                   void* io_buf,
                                   size_t io_block,
-                                  double seconds_per_prng )
+                                  double seconds_per_prng,
+                                  nwipe_prng_live_t* live )
 {
     void* state = NULL;
 
@@ -755,6 +805,13 @@ static void nwipe_prng_bench_one( const nwipe_prng_t* prng,
     const double t0 = nwipe_prng_monotonic_seconds();
     double now = t0;
 
+    /* ensure spinner is visible right when this PRNG starts doing work */
+    if( live && live->enabled && live->is_tty )
+    {
+        live->last_tick = now;
+        nwipe_prng_live_render_spinner( live, /*advance=*/0 );
+    }
+
     while( ( now - t0 ) < seconds_per_prng )
     {
         rc = prng->read( &state, io_buf, io_block );
@@ -766,6 +823,9 @@ static void nwipe_prng_bench_one( const nwipe_prng_t* prng,
 
         out->bytes += (unsigned long long) io_block;
         now = nwipe_prng_monotonic_seconds();
+
+        /* keep the classic cursor rotating while the benchmark runs */
+        nwipe_prng_live_tick_if_due( live, now );
     }
 
     out->seconds = now - t0;
@@ -778,15 +838,18 @@ static void nwipe_prng_bench_one( const nwipe_prng_t* prng,
         free( state );
 }
 
-int nwipe_prng_benchmark_all( double seconds_per_prng,
-                              size_t io_block_bytes,
-                              nwipe_prng_bench_result_t* results,
-                              size_t results_count )
+/* --- new: benchmark all with optional live output ----------------------- */
+
+int nwipe_prng_benchmark_all_live( double seconds_per_prng,
+                                   size_t io_block_bytes,
+                                   nwipe_prng_bench_result_t* results,
+                                   size_t results_count,
+                                   int live_print )
 {
     if( results == NULL || results_count == 0 )
         return 0;
 
-    /* Anzahl PRNGs begrenzen auf results_count */
+    /* limit number of PRNGs to results_count */
     size_t max = sizeof( all_prngs ) / sizeof( all_prngs[0] );
     if( results_count < max )
         max = results_count;
@@ -798,42 +861,107 @@ int nwipe_prng_benchmark_all( double seconds_per_prng,
         return -1;
     }
 
+    nwipe_prng_live_t live;
+    memset( &live, 0, sizeof( live ) );
+    live.enabled = ( live_print ? 1 : 0 );
+    live.is_tty = ( live.enabled ? ( isatty( fileno( stdout ) ) ? 1 : 0 ) : 0 );
+    live.spin_idx = 0;
+    live.last_tick = nwipe_prng_monotonic_seconds();
+    live.analysing_msg = "Analysing PRNG performance:";
+
+    if( live.enabled )
+    {
+        if( live.is_tty )
+        {
+            /* show immediately (user sees activity right away) */
+            nwipe_prng_live_render_spinner( &live, /*advance=*/0 );
+        }
+        else
+        {
+            /* non-interactive: just print the header once */
+            printf( "%s\n", live.analysing_msg );
+            fflush( stdout );
+        }
+    }
+
     for( size_t i = 0; i < max; i++ )
     {
         nwipe_prng_bench_result_t* r = &results[i];
         memset( r, 0, sizeof( *r ) );
-        nwipe_prng_bench_one( all_prngs[i], r, io_buf, io_block_bytes, seconds_per_prng );
+
+        const nwipe_prng_t* prng = all_prngs[i];
+
+        if( live.enabled )
+        {
+            if( live.is_tty )
+                nwipe_prng_live_clear_line( &live );
+
+            /* as requested: print before starting each PRNG */
+            printf( "Testing %s performance...\n", prng->label );
+            fflush( stdout );
+
+            if( live.is_tty )
+            {
+                /* re-show spinner line while the PRNG runs */
+                live.last_tick = nwipe_prng_monotonic_seconds();
+                nwipe_prng_live_render_spinner( &live, /*advance=*/0 );
+            }
+        }
+
+        nwipe_prng_bench_one( prng, r, io_buf, io_block_bytes, seconds_per_prng, &live );
+
+        if( live.enabled )
+        {
+            if( live.is_tty )
+                nwipe_prng_live_clear_line( &live );
+
+            /* print result immediately after each PRNG */
+            if( r->rc == 0 )
+                printf( "%-22s -> %8.1f MB/s\n", r->prng->label, r->mbps );
+            else
+                printf( "%-22s -> (failed: rc=%d)\n", r->prng->label, r->rc );
+            fflush( stdout );
+
+            if( live.is_tty )
+            {
+                /* keep spinner visible between PRNGs */
+                live.last_tick = nwipe_prng_monotonic_seconds();
+                nwipe_prng_live_render_spinner( &live, /*advance=*/1 );
+            }
+        }
+    }
+
+    if( live.enabled && live.is_tty )
+    {
+        /* remove spinner line before subsequent prints (Selected PRNG, GUI, etc.) */
+        nwipe_prng_live_clear_line( &live );
     }
 
     free( io_buf );
     return (int) max;
 }
 
+/* keep old API intact (no live output) */
+int nwipe_prng_benchmark_all( double seconds_per_prng,
+                              size_t io_block_bytes,
+                              nwipe_prng_bench_result_t* results,
+                              size_t results_count )
+{
+    return nwipe_prng_benchmark_all_live( seconds_per_prng, io_block_bytes, results, results_count, /*live_print=*/0 );
+}
+
+/* --- select fastest: now uses live benchmark so printing is not delayed -- */
+
 const nwipe_prng_t* nwipe_prng_select_fastest( double seconds_per_prng,
                                                size_t io_block_bytes,
                                                nwipe_prng_bench_result_t* results,
                                                size_t results_count )
 {
-    int n = nwipe_prng_benchmark_all( seconds_per_prng, io_block_bytes, results, results_count );
+    /* live_print=1 => prints per PRNG immediately (plus spinner) */
+    int n = nwipe_prng_benchmark_all_live( seconds_per_prng, io_block_bytes, results, results_count, /*live_print=*/1 );
     if( n <= 0 )
         return NULL;
 
-    printf( "Analysing PRNG performance:\n" );
-    fflush( stdout );
-
-    for( int i = 0; i < n; i++ )
-    {
-        if( results[i].prng == NULL )
-            continue;
-
-        if( results[i].rc == 0 )
-            printf( "%-22s -> %8.1f MB/s\n", results[i].prng->label, results[i].mbps );
-        else
-            printf( "%-22s -> (failed: rc=%d)\n", results[i].prng->label, results[i].rc );
-
-        fflush( stdout );
-    }
-
     const nwipe_prng_t* best = NULL;
     double best_mbps = 0.0;
 

src/prng.h

@@ -54,11 +54,24 @@ typedef struct
     int rc;
 } nwipe_prng_bench_result_t;
 
+/* Existing API (kept for compatibility: no live output) */
 int nwipe_prng_benchmark_all( double seconds_per_prng,
                               size_t io_block_bytes,
                               nwipe_prng_bench_result_t* results,
                               size_t results_count );
 
+/* New API: live output (spinner + per-PRNG immediate prints)
+ * live_print:
+ *   0 = behave like old benchmark (silent, just fills results[])
+ *   1 = print "Analysing PRNG performance:" immediately, rotate cursor,
+ *       print "Testing <PRNG>..." before each PRNG, and print result right after.
+ */
+int nwipe_prng_benchmark_all_live( double seconds_per_prng,
+                                   size_t io_block_bytes,
+                                   nwipe_prng_bench_result_t* results,
+                                   size_t results_count,
+                                   int live_print );
+
 const nwipe_prng_t* nwipe_prng_select_fastest( double seconds_per_prng,
                                                size_t io_block_bytes,
                                                nwipe_prng_bench_result_t* results,