Try to improve performance by using a multiplication table

2 files changed, 36 insertions, 55 deletions

diff --git a/Makefile b/Makefile
index 816b819..60a141c 100644
--- a/Makefile
+++ b/Makefile
@@ -27,7 +27,7 @@ INC_FLAGS   := $(addprefix -I,$(INC_DIRS))
 INC_FLAGS   += -I$(LIBGBA_SRC)
 
 # Output library names and executables.
-TARGET         := STEPPER-v1.8-dev-18
+TARGET         := STEPPER-v1.8-dev-20
 ELF            := $(BUILD_DIR)/$(TARGET).elf
 BIN            := $(BUILD_DIR)/$(TARGET).gba
 
diff --git a/src/sequencer.c b/src/sequencer.c
index f8b4a58..45fc0e4 100644
--- a/src/sequencer.c
+++ b/src/sequencer.c
@@ -347,14 +347,32 @@ play_step(void) {
 
 static int nseq_ticks = 0;
 
-UNROLL_LOOPS
 IWRAM_CODE
+UNROLL_LOOPS
 void
 wave_ad_tick(void) {
     Wave wave_active = {0};
     Wave wave_zero = {
         0x77777777, 0x77777777, 0x77777777, 0x77777777,
     };
+    const u8 mult_table[16][8] = {
+        {7,  5,  4,  3,  2,  1,  1,  0},
+        {7,  6,  5,  4,  3,  2,  2,  1},
+        {7,  6,  5,  4,  4,  3,  2,  2},
+        {7,  6,  5,  5,  4,  4,  3,  3},
+        {7,  6,  6,  5,  5,  5,  4,  4},
+        {7,  7,  6,  6,  6,  5,  5,  5},
+        {7,  7,  7,  6,  6,  6,  6,  6},
+        {7,  7,  7,  7,  7,  7,  7,  7},
+        {7,  7,  7,  8,  8,  8,  8,  8},
+        {7,  7,  8,  8,  8,  9,  9,  9},
+        {7,  8,  8,  9,  9,  9, 10, 10},
+        {7,  8,  9,  9, 10, 10, 11, 11},
+        {7,  8,  9, 10, 10, 11, 12, 12},
+        {7,  8,  9, 10, 11, 12, 12, 13},
+        {7,  9, 10, 11, 12, 13, 13, 14},
+        {7,  9, 10, 11, 13, 13, 14, 15},
+    };
 env_start:
     switch (wave_env) {
         case WAV_ENV_START: {
@@ -394,42 +412,24 @@ env_start:
             wave_env_ticks = 0;
 
             // Attack.
-            int powers[] = {
-                20,  57, 104, 143, 177, 208, 235, 256,
-            };
-            int power = powers[wave_env_prog];
-            if (++wave_env_prog >= 8) {
-                if (wave_env_decay == 0) {
-                    wave_env = WAV_ENV_OFF;
-                } else {
-                    wave_env = WAV_ENV_DECAY;
-                }
-                wave_env_prog = 0;
-            }
             for (size_t j = 0; j < 4; j++) {
                 u32 next = 0;
                 u32 prev = (*wave_target)[j];
                 for (size_t i = 0; i < 8; i++) {
                     u8 val = (prev >> 4 * i) & 0xF;
-                    // Operating in 24.8 fixed point:
-                    if (val < 0x7) {
-                        int tmp = 0x7 - val;
-                        tmp *= power;
-                        tmp >>= 8;
-                        val = (0x7 - tmp) & 0xf;
-                    } else if (val > 0x7) {
-                        int tmp = (val - 0x7);
-                        tmp *= power;
-                        tmp >>= 8;
-                        val = tmp + 0x7;
-                        if (val <= 0x7) {
-                            val = 0x7;
-                        }
-                    }
-                    next |= (val << 4 * i);
+                    u8 tmp = mult_table[val][wave_env_prog];
+                    next |= (tmp << 4 * i);
                 }
                 wave_active[j] = next;
             }
+            if (++wave_env_prog >= 8) {
+                if (wave_env_decay == 0) {
+                    wave_env = WAV_ENV_OFF;
+                } else {
+                    wave_env = WAV_ENV_DECAY;
+                }
+                wave_env_prog = 0;
+            }
 
             // DEBUG:
             // int x = 50;
@@ -447,39 +447,20 @@ env_start:
             wave_env_ticks = 0;
 
             // Decay.
-            int powers[] = {
-                // Logarithmic volume range.
-                256, 235, 208, 177, 143, 104, 57, 0
-            };
-            int power = powers[wave_env_prog];
-            if (++wave_env_prog >= 8) {
-                wave_env = WAV_ENV_END;
-                wave_env_prog = 0;
-            }
             for (size_t j = 0; j < 4; j++) {
                 u32 next = 0;
                 u32 prev = (*wave_target)[j];
                 for (size_t i = 0; i < 8; i++) {
                     u8 val = (prev >> 4 * i) & 0xF;
-                    // Operating in 24.8 fixed point:
-                    if (val < 0x7) {
-                        int tmp = 0x7 - val;
-                        tmp *= power;
-                        tmp >>= 8;
-                        val = (0x7 - tmp) & 0xf;
-                    } else if (val > 0x7) {
-                        int tmp = (val - 0x7);
-                        tmp *= power;
-                        tmp >>= 8;
-                        val = tmp + 0x7;
-                        if (val <= 0x7) {
-                            val = 0x7;
-                        }
-                    }
-                    next |= (val << 4 * i);
+                    u8 tmp = mult_table[val][7 - wave_env_prog];
+                    next |= (tmp << 4 * i);
                 }
                 wave_active[j] = next;
             }
+            if (++wave_env_prog >= 8) {
+                wave_env = WAV_ENV_END;
+                wave_env_prog = 0;
+            }
 
             // DEBUG:
             // int x = 50;