From 258c89151ce1d76357096bf73590bfc23832596b Mon Sep 17 00:00:00 2001
From: pixel-jupiter <180155003+pixel-jupiter@users.noreply.github.com>
Date: Fri, 24 Oct 2025 01:12:26 +0300
Subject: [PATCH] Optimize negative bounds checking in rendering loops

---
 src/video/vid_tandy.c | 257 ++++++++++++++++++++++++------------------
 1 file changed, 147 insertions(+), 110 deletions(-)

diff --git a/src/video/vid_tandy.c b/src/video/vid_tandy.c
index 14d6d8e69..3d2be3a41 100644
--- a/src/video/vid_tandy.c
+++ b/src/video/vid_tandy.c
@@ -396,37 +396,51 @@ vid_render(tandy_t *dev, int line, int hos_offs)
     uint16_t  dat;
     int       col;
     int       cols[4];
+    uint32_t  border_val;
     int       out_x;
+    int       c_start;
 
     cols[0]       = (vid->array[2] & 0xf) + 16;
 
-    if (line >= 0) {
+    if (line < 0) {
+        if (dev->is_sl2 && (vid->array[5] & 1)) {
+            vid->memaddr += vid->crtc[1] * 2;
+        } else {
+            vid->memaddr += vid->crtc[1];
+        }
+        return;
+    }
+
+    if (vid->array[3] & 4) {
+        border_val = cols[0];
+    } else if ((vid->mode & 0x12) == 0x12) {
+        border_val = 0;
+    } else {
+        border_val = (vid->col & 15) + 16;
+    }
+
+    if (vid->array[3] & 4) {
         for (c = 0; c < hos_offs; c++) {
-            if (vid->array[3] & 4) {
-                    buffer32->line[line][c] = cols[0];
-            } else if ((vid->mode & 0x12) == 0x12) {
-                    buffer32->line[line][c] = 0;
-            } else {
-                    buffer32->line[line][c] = buffer32->line[(line) + 1][c] = (vid->col & 15) + 16;
-            }
+            buffer32->line[line][c] = border_val;
         }
-
-        for (c = 0; c < 8 - vid->hsync_offset; c++) {
-            if (vid->mode & 1)
-                out_x = c + (vid->crtc[1] << 3) + hos_offs;
-            else
-                out_x = c + (vid->crtc[1] << 4) + hos_offs;
-
-            if (out_x >= 0) {
-                if (vid->array[3] & 4) {
-                    buffer32->line[line][out_x] = cols[0];
-                } else if ((vid->mode & 0x12) == 0x12) {
-                    buffer32->line[line][out_x] = 0;
-                } else {
-                    buffer32->line[line][out_x] = (vid->col & 15) + 16;
-                }
-            }
+    } else if ((vid->mode & 0x12) == 0x12) {
+        for (c = 0; c < hos_offs; c++) {
+            buffer32->line[line][c] = border_val;
         }
+    } else {
+        for (c = 0; c < hos_offs; c++) {
+            buffer32->line[line][c] = buffer32->line[(line) + 1][c] = border_val;
+        }
+    }
+
+    if (vid->mode & 1) {
+        out_x = (vid->crtc[1] << 3) + hos_offs;
+    } else {
+        out_x = (vid->crtc[1] << 4) + hos_offs;
+    }
+    c_start = out_x < 0 ? -out_x : 0;
+    for (c = c_start; c < 8 - vid->hsync_offset; c++) {
+        buffer32->line[line][out_x + c] = border_val;
     }
 
     if (dev->is_sl2 && (vid->array[5] & 1)) { /*640x200x16*/
@@ -434,11 +448,16 @@ vid_render(tandy_t *dev, int line, int hos_offs)
             dat = (vid->vram[(vid->memaddr << 1) & 0xffff] << 8) | vid->vram[((vid->memaddr << 1) + 1) & 0xffff];
             vid->memaddr++;
             out_x = (x << 2) + hos_offs;
-            if (line >= 0) {
-                if (out_x >= 0)     buffer32->line[line][out_x]     = vid->array[((dat >> 12) & 0xf) + 16] + 16;
-                if (out_x + 1 >= 0) buffer32->line[line][out_x + 1] = vid->array[((dat >> 8) & 0xf) + 16] + 16;
-                if (out_x + 2 >= 0) buffer32->line[line][out_x + 2] = vid->array[((dat >> 4) & 0xf) + 16] + 16;
-                if (out_x + 3 >= 0) buffer32->line[line][out_x + 3] = vid->array[(dat & 0xf) + 16] + 16;
+            if (out_x >= 0) {
+                buffer32->line[line][out_x]     = vid->array[((dat >> 12) & 0xf) + 16] + 16;
+                buffer32->line[line][out_x + 1] = vid->array[((dat >> 8) & 0xf) + 16] + 16;
+                buffer32->line[line][out_x + 2] = vid->array[((dat >> 4) & 0xf) + 16] + 16;
+                buffer32->line[line][out_x + 3] = vid->array[(dat & 0xf) + 16] + 16;
+            } else if (out_x > -4) {
+                for (c = -out_x; c < 4; c++) {
+                    buffer32->line[line][out_x + c] =
+                        vid->array[((dat >> (12 - c * 4)) & 0xf) + 16] + 16;
+                }
             }
         }
     } else if ((vid->array[3] & 0x10) && (vid->mode & 1)) { /*320x200x16*/
@@ -447,15 +466,20 @@ vid_render(tandy_t *dev, int line, int hos_offs)
                   vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 3) * 0x2000) + 1];
             vid->memaddr++;
             out_x = (x << 3) + hos_offs;
-            if (line >= 0) {
-                if (out_x >= 0)     buffer32->line[line][out_x] = buffer32->line[line][out_x + 1] =
+            if (out_x >= 0) {
+                buffer32->line[line][out_x]     = buffer32->line[line][out_x + 1] =
                     vid->array[((dat >> 12) & vid->array[1] & 0x0f) + 16] + 16;
-                if (out_x + 2 >= 0) buffer32->line[line][out_x + 2] = buffer32->line[line][out_x + 3] =
+                buffer32->line[line][out_x + 2] = buffer32->line[line][out_x + 3] =
                     vid->array[((dat >> 8) & vid->array[1] & 0x0f) + 16] + 16;
-                if (out_x + 4 >= 0) buffer32->line[line][out_x + 4] = buffer32->line[line][out_x + 5] =
+                buffer32->line[line][out_x + 4] = buffer32->line[line][out_x + 5] =
                     vid->array[((dat >> 4) & vid->array[1] & 0x0f) + 16] + 16;
-                if (out_x + 6 >= 0) buffer32->line[line][out_x + 6] = buffer32->line[line][out_x + 7] =
+                buffer32->line[line][out_x + 6] = buffer32->line[line][out_x + 7] =
                     vid->array[(dat & vid->array[1] & 0x0f) + 16] + 16;
+            } else if (out_x > -8) {
+                for (c = -out_x; c < 8; c++) {
+                    buffer32->line[line][out_x + c] =
+                        vid->array[((dat >> 12 - (c >> 1) * 4) & vid->array[1] & 0x0f) + 16] + 16;
+                }
             }
         }
     } else if (vid->array[3] & 0x10) { /*160x200x16*/
@@ -468,19 +492,24 @@ vid_render(tandy_t *dev, int line, int hos_offs)
                       vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 3) * 0x2000) + 1];
             vid->memaddr++;
             out_x = (x << 4) + hos_offs;
-            if (line >= 0) {
-                if (out_x >= 0)      buffer32->line[line][out_x] = buffer32->line[line][out_x + 1] =
-                buffer32->line[line][out_x + 2] = buffer32->line[line][out_x + 3] =
+            if (out_x >= 0) {
+                buffer32->line[line][out_x]      = buffer32->line[line][out_x + 1]  =
+                buffer32->line[line][out_x + 2]  = buffer32->line[line][out_x + 3]  =
                     vid->array[((dat >> 12) & vid->array[1] & 0x0f) + 16] + 16;
-                if (out_x + 4 >= 0)  buffer32->line[line][out_x + 4] = buffer32->line[line][out_x + 5] =
-                buffer32->line[line][out_x + 6] = buffer32->line[line][out_x + 7] =
+                buffer32->line[line][out_x + 4]  = buffer32->line[line][out_x + 5]  =
+                buffer32->line[line][out_x + 6]  = buffer32->line[line][out_x + 7]  =
                     vid->array[((dat >> 8) & vid->array[1] & 0x0f) + 16] + 16;
-                if (out_x + 8 >= 0)  buffer32->line[line][out_x + 8] = buffer32->line[line][out_x + 9] =
+                buffer32->line[line][out_x + 8]  = buffer32->line[line][out_x + 9]  =
                 buffer32->line[line][out_x + 10] = buffer32->line[line][out_x + 11] =
                     vid->array[((dat >> 4) & vid->array[1] & 0x0f) + 16] + 16;
-                if (out_x + 12 >= 0) buffer32->line[line][out_x + 12] = buffer32->line[line][out_x + 13] =
+                buffer32->line[line][out_x + 12] = buffer32->line[line][out_x + 13] =
                 buffer32->line[line][out_x + 14] = buffer32->line[line][out_x + 15] =
                     vid->array[(dat & vid->array[1] & 0x0f) + 16] + 16;
+            } else if (out_x > -16) {
+                for (c = -out_x; c < 16; c++) {
+                    buffer32->line[line][out_x + c] =
+                        vid->array[((dat >> 12 - (c >> 2) * 4) & vid->array[1] & 0x0f) + 16] + 16;
+                }
             }
         }
     } else if (vid->array[3] & 0x08) { /*640x200x4 - this implementation is a complete guess!*/
@@ -488,14 +517,17 @@ vid_render(tandy_t *dev, int line, int hos_offs)
             dat = (vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 3) * 0x2000)] << 8) |
                   vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 3) * 0x2000) + 1];
             vid->memaddr++;
-            for (c = 0; c < 8; c++) {
-                chr = (dat >> 6) & 2;
-                chr |= ((dat >> 15) & 1);
-                out_x = (x << 3) + hos_offs + c;
-                if (out_x >= 0 && line >= 0)
-                    buffer32->line[line][out_x] =
+            out_x = (x << 3) + hos_offs;
+            if (out_x > -8) {
+                c_start = out_x < 0 ? -out_x : 0;
+                dat <<= c_start;
+                for (c = c_start; c < 8; c++) {
+                    chr = (dat >> 6) & 2;
+                    chr |= ((dat >> 15) & 1);
+                    buffer32->line[line][out_x + c] =
                         vid->array[(chr & vid->array[1]) + 16] + 16;
-                dat <<= 1;
+                    dat <<= 1;
+                }
             }
         }
     } else if (vid->mode & 1) {
@@ -512,25 +544,20 @@ vid_render(tandy_t *dev, int line, int hos_offs)
                 cols[1] = vid->array[((attr & 15) & vid->array[1]) + 16] + 16;
                 cols[0] = vid->array[((attr >> 4) & vid->array[1]) + 16] + 16;
             }
-            if (line >= 0) {
-                if (vid->scanline & 8)  for (c = 0; c < 8; c++) {
-                    out_x = (x << 3) + c + hos_offs;
-                    if (out_x >= 0)
-                        buffer32->line[line][out_x] =
-                            ((chr >= 0xb3) && (chr <= 0xdf)) ? cols[(fontdat[chr][7] & (1 << (c ^ 7))) ? 1 : 0] : cols[0];
-                } else  for (c = 0; c < 8; c++) {
-                    out_x = (x << 3) + c + hos_offs;
-                    if (out_x >= 0) {
-                        if (vid->scanline == 8)
-                            buffer32->line[line][out_x] = cols[(fontdat[chr][7] & (1 << (c ^ 7))) ? 1 : 0];
-                        else
-                            buffer32->line[line][out_x] = cols[(fontdat[chr][vid->scanline & 7] & (1 << (c ^ 7))) ? 1 : 0];
-                    }
+            out_x = (x << 3) + hos_offs;
+            if (out_x > -8) {
+                c_start = out_x < 0 ? -out_x : 0;
+                if (vid->scanline & 8)  for (c = c_start; c < 8; c++) {
+                    buffer32->line[line][out_x + c] =
+                        ((chr >= 0xb3) && (chr <= 0xdf)) ? cols[(fontdat[chr][7] & (1 << (c ^ 7))) ? 1 : 0] : cols[0];
+                } else  for (c = c_start; c < 8; c++) {
+                    if (vid->scanline == 8)
+                        buffer32->line[line][out_x + c] = cols[(fontdat[chr][7] & (1 << (c ^ 7))) ? 1 : 0];
+                    else
+                        buffer32->line[line][out_x + c] = cols[(fontdat[chr][vid->scanline & 7] & (1 << (c ^ 7))) ? 1 : 0];
                 }
-                if (drawcursor)  for (c = 0; c < 8; c++) {
-                    out_x = (x << 3) + c + hos_offs;
-                    if (out_x >= 0)
-                        buffer32->line[line][out_x] ^= 15;
+                if (drawcursor)  for (c = c_start; c < 8; c++) {
+                    buffer32->line[line][out_x + c] ^= 15;
                 }
             }
             vid->memaddr++;
@@ -550,28 +577,29 @@ vid_render(tandy_t *dev, int line, int hos_offs)
                 cols[0] = vid->array[((attr >> 4) & vid->array[1]) + 16] + 16;
             }
             vid->memaddr++;
-            if (line >= 0) {
-                if (vid->scanline & 8)  for (c = 0; c < 8; c++) {
-                    out_x = (x << 4) + (c << 1) + hos_offs;
-                    if (out_x >= 0)     buffer32->line[line][out_x] =
-                        buffer32->line[line][out_x + 1] =
+            out_x = (x << 4) + hos_offs;
+            if (out_x > -16) {
+                c_start = out_x < 0 ? -out_x >> 1 : 0;
+                if (vid->scanline & 8)  for (c = c_start; c < 8; c++) {
+                    buffer32->line[line][out_x + (c << 1)] =
+                    buffer32->line[line][out_x + 1 + (c << 1)] =
                         ((chr >= 0xb3) && (chr <= 0xdf)) ? cols[(fontdat[chr][7] & (1 << (c ^ 7))) ? 1 : 0] : cols[0];
-                } else  for (c = 0; c < 8; c++) {
-                    out_x = (x << 4) + (c << 1) + hos_offs;
+                } else  for (c = c_start; c < 8; c++) {
                     if (vid->scanline == 8) {
-                        if (out_x >= 0)     buffer32->line[line][out_x] =
-                            buffer32->line[line][out_x + 1] =
+                        buffer32->line[line][out_x + (c << 1)] =
+                        buffer32->line[line][out_x + 1 + (c << 1)] =
                             cols[(fontdat[chr][7] & (1 << (c ^ 7))) ? 1 : 0];
                     } else {
-                        if (out_x >= 0)     buffer32->line[line][out_x] =
-                            buffer32->line[line][out_x + 1] =
+                        buffer32->line[line][out_x + (c << 1)] =
+                        buffer32->line[line][out_x + 1 + (c << 1)] =
                             cols[(fontdat[chr][vid->scanline & 7] & (1 << (c ^ 7))) ? 1 : 0];
                     }
                 }
-                if (drawcursor)  for (c = 0; c < 16; c++) {
-                    out_x = (x << 4) + c + hos_offs;
-                    if (out_x >= 0)
-                        buffer32->line[line][out_x] ^= 15;
+                if (drawcursor) {
+                    c_start = out_x < 0 ? -out_x : 0;
+                    for (c = c_start; c < 16; c++) {
+                        buffer32->line[line][out_x + c] ^= 15;
+                    }
                 }
             }
         }
@@ -599,11 +627,15 @@ vid_render(tandy_t *dev, int line, int hos_offs)
             dat = (vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 1) * 0x2000)] << 8) |
                   vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 1) * 0x2000) + 1];
             vid->memaddr++;
-            for (c = 0; c < 8; c++) {
-                out_x = (x << 4) + (c << 1) + hos_offs;
-                if (out_x >= 0 && line >= 0)     buffer32->line[line][out_x] =
-                buffer32->line[line][out_x + 1] = cols[dat >> 14];
-                dat <<= 2;
+            out_x = (x << 4) + hos_offs;
+            if (out_x > -16) {
+                c_start = out_x < 0 ? -out_x >> 1 : 0;
+                dat <<= (c_start > 0 ? c_start << 1 : 0);
+                for (c = c_start; c < 8; c++) {
+                    buffer32->line[line][out_x + (c << 1)] =
+                    buffer32->line[line][out_x + 1 + (c << 1)] = cols[dat >> 14];
+                    dat <<= 2;
+                }
             }
         }
     } else {
@@ -613,11 +645,14 @@ vid_render(tandy_t *dev, int line, int hos_offs)
             dat = (vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 1) * 0x2000)] << 8) |
                   vid->vram[((vid->memaddr << 1) & 0x1fff) + ((vid->scanline & 1) * 0x2000) + 1];
             vid->memaddr++;
-            for (c = 0; c < 16; c++) {
-                out_x = (x << 4) + c + hos_offs;
-                if (out_x >= 0 && line >= 0)
-                    buffer32->line[line][out_x] = buffer32->line[(line) + 1][out_x] = cols[dat >> 15];
-                dat <<= 1;
+            out_x = (x << 4) + hos_offs;
+            if (out_x > -16) {
+                c_start = out_x < 0 ? -out_x : 0;
+                dat <<= (c_start > 0 ? c_start : 0);
+                for (c = c_start; c < 16; c++) {
+                    buffer32->line[line][out_x + c] = buffer32->line[(line) + 1][out_x + c] = cols[dat >> 15];
+                    dat <<= 1;
+                }
             }
         }
     }
@@ -628,20 +663,21 @@ vid_render_blank(tandy_t *dev, int line)
 {
     t1kvid_t *vid         = dev->vid;
 
-    if (line >= 0) {
-        if (vid->array[3] & 4) {
-            if (vid->mode & 1)
-                hline(buffer32, 0, line, (vid->crtc[1] << 3) + 16, (vid->array[2] & 0xf) + 16);
-            else
-                hline(buffer32, 0, line, (vid->crtc[1] << 4) + 16, (vid->array[2] & 0xf) + 16);
-        } else {
-            int cols = ((vid->mode & 0x12) == 0x12) ? 0 : (vid->col & 0xf) + 16;
+    if (line < 0)
+        return;
 
-            if (vid->mode & 1)
-                hline(buffer32, 0, line, (vid->crtc[1] << 3) + 16, cols);
-            else
-                hline(buffer32, 0, line, (vid->crtc[1] << 4) + 16, cols);
-        }
+    if (vid->array[3] & 4) {
+        if (vid->mode & 1)
+            hline(buffer32, 0, line, (vid->crtc[1] << 3) + 16, (vid->array[2] & 0xf) + 16);
+        else
+            hline(buffer32, 0, line, (vid->crtc[1] << 4) + 16, (vid->array[2] & 0xf) + 16);
+    } else {
+        int cols = ((vid->mode & 0x12) == 0x12) ? 0 : (vid->col & 0xf) + 16;
+
+        if (vid->mode & 1)
+            hline(buffer32, 0, line, (vid->crtc[1] << 3) + 16, cols);
+        else
+            hline(buffer32, 0, line, (vid->crtc[1] << 4) + 16, cols);
     }
 }
 
@@ -651,17 +687,18 @@ vid_render_process(tandy_t *dev, int line)
     t1kvid_t *vid         = dev->vid;
     int       x;
 
+    if (line < 0)
+        return;
+
     if (vid->mode & 1)
         x = (vid->crtc[1] << 3) + 16;
     else
         x = (vid->crtc[1] << 4) + 16;
 
-    if (line >= 0) {
-        if (!dev->is_sl2 && vid->composite)
-            Composite_Process(vid->mode, 0, x >> 2, buffer32->line[line]);
-        else
-            video_process_8(x, line);
-    }
+    if (!dev->is_sl2 && vid->composite)
+        Composite_Process(vid->mode, 0, x >> 2, buffer32->line[line]);
+    else
+        video_process_8(x, line);
 }
 
 static void