diff --git a/include/functions.h b/include/functions.h
index 8ac7e3e4d3..3d9a0912ea 100644
--- a/include/functions.h
+++ b/include/functions.h
@@ -33,10 +33,10 @@ s32 DmaMgr_SendRequestImpl(DmaRequest* request, void* vramStart, u32 vromStart,
 s32 DmaMgr_SendRequest0(void* vramStart, u32 vromStart, u32 size);
 void Dmamgr_Start(void);
 void Dmamgr_Stop(void);
-// u8* Yaz0_LoadFirstChunk(void);
-u8* Yaz0_LoadNextChunk(void* currDecompPos);
-s32 Yaz0_Decompress(u8* src, u8* dest);
-void Yaz0_LoadAndDecompressFile(u32 romStart, u32 vramStart, u32 size);
+void* Yaz0_FirstDMA(void);
+void* Yaz0_NextDMA(void* curSrcPos);
+s32 Yaz0_DecompressImpl(u8* hdr, u8* dst);
+void Yaz0_Decompress(u32 romStart, void* dst, u32 size);
 void IrqMgr_AddClient(IrqMgr* irqmgr, OSMesgQueueListNode* param_2, OSMesgQueue* param_3);
 void IrqMgr_RemoveClient(IrqMgr* irqmgr, OSMesgQueueListNode* remove);
 void IrqMgr_SendMesgForClient(IrqMgr* irqmgr, OSMesg msg);
@@ -247,7 +247,7 @@ s32 sprintf(char* s, char* fmt, ...);
 // void func_80087934(void);
 void wait_cycles(OSTime uParm1);
 // void func_800879CC(void);
-// void func_80087A1C(void);
+void func_80087A1C(UNK_TYPE);
 void func_80087A6C(u32 param_1);
 // void func_80087AC0(void);
 // void __osSetCause(void);
@@ -418,7 +418,7 @@ void __osSetCompare(u32 value);
 // u32 __osGetCompare(void);
 u32 osDpGetStatus(void);
 void osDpSetStatus(u32 data);
-void _bcopy(void* __src, void* __dest, size_t __n);
+void bcopy(void* __src, void* __dest, size_t __n);
 // void __osResetGlobalIntMask(void);
 // void func_80091630(UNK_TYPE1 param_1, UNK_TYPE1 param_2, UNK_TYPE1 param_3, UNK_TYPE1 param_4, UNK_TYPE4 param_5);
 // void func_80091808(UNK_TYPE1 param_1, UNK_TYPE1 param_2, UNK_TYPE1 param_3, UNK_TYPE1 param_4, UNK_TYPE4 param_5);
diff --git a/include/variables.h b/include/variables.h
index 3086fee9b6..ccb145a9a4 100644
--- a/include/variables.h
+++ b/include/variables.h
@@ -295,8 +295,12 @@ extern OSMesg dmamgrMsqMessages[32];
 extern OSThread dmamgrOSThread;
 extern u8 dmamgrStack[1280];
 // extern UNK_TYPE1 D_8009BA08;
-extern u8 yaz0FileBuffer[1024];
-extern Yaz0DecompState yaz0DecompStatus;
+extern u8 sYaz0DataBuffer[0x400];
+extern u8* sYaz0CurDataEnd;
+extern u32 sYaz0CurRomStart;
+extern u32 sYaz0CurSize;
+extern u8* sYaz0MaxPtr;
+extern u8* D_8009BE20;
 extern UNK_TYPE4 D_8009BE30;
 extern UNK_TYPE4 D_8009BE34;
 extern FaultClient romInfoFaultClient;
diff --git a/include/z64.h b/include/z64.h
index 16161284fb..27001572bf 100644
--- a/include/z64.h
+++ b/include/z64.h
@@ -431,14 +431,6 @@ typedef struct {
     /* 0xC */ s32 rightX;
 } Viewport; // size = 0x10
 
-typedef struct {
-    /* 0x00 */ void* bufferEnd;
-    /* 0x04 */ u32 romReadHead;
-    /* 0x08 */ u32 amountLeftToRead;
-    /* 0x0C */ u32 loadNextChunkBoundary;
-    /* 0x10 */ u32 destBufferEnd;
-} Yaz0DecompState; // size = 0x14
-
 typedef struct {
     /* 0x0 */ unsigned int inst1;
     /* 0x4 */ unsigned int inst2;
diff --git a/linker_scripts/code_script.txt b/linker_scripts/code_script.txt
index 66b0b32216..0bcd1325c9 100644
--- a/linker_scripts/code_script.txt
+++ b/linker_scripts/code_script.txt
@@ -15,7 +15,7 @@ SECTIONS
         build/src/boot_O2_g3/idle.o(.text)
         build/src/boot_O2_g3/viconfig.o(.text)
         build/src/boot_O2_g3/z_std_dma.o(.text)
-        build/asm/boot/boot_0x80080E30.o(.text)
+        build/src/boot_O2_g3/yaz0.o(.text)
         build/src/boot_O2_g3/irqmgr.o(.text)
         build/src/boot_O2_g3/CIC6105.o(.text)
         build/src/boot_O2_g3/boot_0x80081920.o(.text)
@@ -252,7 +252,7 @@ SECTIONS
         build/src/boot_O2_g3/boot_main.o(.rodata)
         build/src/boot_O2_g3/idle.o(.rodata)
         build/asm/boot/boot_rodata_z_std_dma.o(.rodata)
-        build/asm/boot/boot_rodata_0x80080E30.o(.rodata)
+        build/src/boot_O2_g3/yaz0.o(.rodata)
         build/src/boot_O2_g3/irqmgr.o(.rodata)
         build/src/boot_O2_g3/CIC6105.o(.rodata)
         build/asm/boot/boot_rodata_fault.o(.rodata)
@@ -284,7 +284,7 @@ SECTIONS
     . += 0x1C60; /* boot_main */
     . += 0x140; /* idle */
     . += 0x770; /* z_std_dma */
-    . += 0x420; /* 0x80080E30 */
+    . += 0x420; /* yaz0 */
     . += 0x20; /* CIC6105 */
     . += 0xE80; /* fault */
     . += 0x40; /* fault_drawer */
diff --git a/src/boot_O2_g3/yaz0.c b/src/boot_O2_g3/yaz0.c
new file mode 100644
index 0000000000..e583a086f5
--- /dev/null
+++ b/src/boot_O2_g3/yaz0.c
@@ -0,0 +1,150 @@
+#include <ultra64.h>
+#include <global.h>
+
+u8 sYaz0DataBuffer[0x400];
+u8* sYaz0CurDataEnd;
+u32 sYaz0CurRomStart;
+u32 sYaz0CurSize;
+u8* sYaz0MaxPtr;
+u8* D_8009BE20;
+
+void* Yaz0_FirstDMA() {
+    u32 pad0;
+    u32 dmaSize;
+    u32 curSize;
+
+    sYaz0MaxPtr = sYaz0CurDataEnd - 0x19;
+
+    curSize = (u32)sYaz0CurDataEnd - (u32)sYaz0DataBuffer;
+    dmaSize = (curSize > sYaz0CurSize) ? sYaz0CurSize : curSize;
+
+    DmaMgr_DMARomToRam(sYaz0CurRomStart, sYaz0DataBuffer, dmaSize);
+    sYaz0CurRomStart += dmaSize;
+    sYaz0CurSize -= dmaSize;
+    return sYaz0DataBuffer;
+}
+
+void* Yaz0_NextDMA(void* curSrcPos) {
+    u8* dst;
+    u32 restSize;
+    u32 dmaSize;
+    OSPri oldPri;
+
+    restSize = (u32)sYaz0CurDataEnd - (u32)curSrcPos;
+
+    dst = (restSize & 7) ? (sYaz0DataBuffer - (restSize & 7)) + 8 : sYaz0DataBuffer;
+
+    bcopy(curSrcPos, dst, restSize);
+    dmaSize = ((u32)sYaz0CurDataEnd - (u32)dst) - restSize;
+    if (sYaz0CurSize < dmaSize) {
+        dmaSize = sYaz0CurSize;
+    }
+
+    if (dmaSize != 0) {
+        DmaMgr_DMARomToRam(sYaz0CurRomStart, dst + restSize, dmaSize);
+        sYaz0CurRomStart += dmaSize;
+        sYaz0CurSize -= dmaSize;
+        if (!sYaz0CurSize) {
+            sYaz0MaxPtr = dst + restSize + dmaSize;
+        }
+    } else {
+        oldPri = osGetThreadPri(NULL);
+        osSetThreadPri(NULL, 0x7F);
+        Fault_Log("圧縮展開異常\n");
+        osSetThreadPri(NULL, oldPri);
+    }
+
+    return dst;
+}
+
+typedef struct {
+    /* 0x00 */ u32 magic; // Yaz0
+    /* 0x04 */ u32 decSize;
+    /* 0x08 */ u32 compInfoOffset; // only used in mio0
+    /* 0x0C */ u32 uncompDataOffset; // only used in mio0
+} Yaz0Header; // size = 0x10
+
+#define YAZ0_MAGIC 0x59617A30 // "Yaz0"
+
+s32 Yaz0_DecompressImpl(u8* src, u8* dst) {
+    u32 bitIdx = 0;
+    u8* dstEnd;
+    u32 chunkHeader = 0;
+    u32 nibble;
+    u8* backPtr;
+    s32 chunkSize;
+    u32 off;
+    u32 magic;
+
+    magic = ((Yaz0Header*)src)->magic;
+
+    if (magic != YAZ0_MAGIC) {
+        return -1;
+    }
+
+    dstEnd = dst + ((Yaz0Header*)src)->decSize;
+    src = src + sizeof(Yaz0Header);
+
+    do {
+        if (bitIdx == 0) {
+            if ((sYaz0MaxPtr < src) && (sYaz0CurSize != 0)) {
+                src = Yaz0_NextDMA(src);
+            }
+
+            chunkHeader = *src++;
+            bitIdx = 8;
+        }
+
+        if (chunkHeader & (1 << 7)) { // uncompressed
+            *dst = *src;
+            dst++;
+            src++;
+        } else { // compressed
+            off = ((*src & 0xF) << 8 | *(src + 1));
+            nibble = *src >> 4;
+            backPtr = dst - off;
+            src += 2;
+
+            chunkSize = (nibble == 0)       // N = chunkSize; B = back offset
+                            ? *src++ + 0x12 // 3 bytes 0B BB NN
+                            : nibble + 2;   // 2 bytes NB BB
+
+            do {
+                *dst++ = *(backPtr++ - 1);
+                chunkSize--;
+            } while (chunkSize != 0);
+        }
+        chunkHeader <<= 1;
+        bitIdx--;
+    } while (dst != dstEnd);
+
+    D_8009BE20 = dstEnd;
+
+    return 0;
+}
+
+void Yaz0_Decompress(u32 romStart, void* dst, u32 size) {
+    s32 status;
+    u32 pad;
+    u8 sp80[0x50];
+    u8 sp30[0x50];
+
+    if (sYaz0CurDataEnd != NULL) {
+        while (sYaz0CurDataEnd != NULL) {
+            func_80087A1C(10);
+        }
+    }
+
+    sYaz0CurDataEnd = sYaz0DataBuffer + sizeof(sYaz0DataBuffer);
+    sYaz0CurRomStart = romStart;
+    sYaz0CurSize = size;
+    status = Yaz0_DecompressImpl(Yaz0_FirstDMA(), dst);
+
+    if (status != 0) {
+        sprintf(sp80, "slidma slidstart_szs ret=%d", status);
+        sprintf(sp30, "src:%08lx dst:%08lx siz:%08lx", romStart, dst, size);
+        Fault_AddHungupAndCrashImpl(sp80, sp30);
+    }
+
+    sYaz0CurDataEnd = NULL;
+}
diff --git a/src/boot_O2_g3/z_std_dma.c b/src/boot_O2_g3/z_std_dma.c
index 6b70433962..2f617eb032 100644
--- a/src/boot_O2_g3/z_std_dma.c
+++ b/src/boot_O2_g3/z_std_dma.c
@@ -134,7 +134,7 @@ void DmaMgr_ProcessMsg(DmaRequest* a0) {
         }
 
         osSetThreadPri(NULL, 10);
-        Yaz0_LoadAndDecompressFile(sp28, sp30, sp24);
+        Yaz0_Decompress(sp28, sp30, sp24);
         osSetThreadPri(NULL, 17);
     } else {
         Fault_AddHungupAndCrash(dmamgrString800981F4, 558);
diff --git a/src/boot_O2_g3_trapuv/fault_drawer.c b/src/boot_O2_g3_trapuv/fault_drawer.c
index b5710aba29..9648ca5aac 100644
--- a/src/boot_O2_g3_trapuv/fault_drawer.c
+++ b/src/boot_O2_g3_trapuv/fault_drawer.c
@@ -132,7 +132,7 @@ void FaultDrawer_SetInputCallback(void(*callback)()) {
 
 void FaultDrawer_Init() {
     sFaultDrawContext = &sFaultDrawerStruct;
-    _bcopy(&sFaultDrawerDefault, sFaultDrawContext, sizeof(FaultDrawer));
+    bcopy(&sFaultDrawerDefault, sFaultDrawContext, sizeof(FaultDrawer));
     sFaultDrawContext->fb = (u16*)((osMemSize | 0x80000000) - 0x25800);
 }
 
diff --git a/src/code/z_lib.c b/src/code/z_lib.c
index fb02269fae..cb48e72d31 100644
--- a/src/code/z_lib.c
+++ b/src/code/z_lib.c
@@ -2,7 +2,7 @@
 #include <global.h>
 
 void* Lib_bcopy(void* dest, void* src, size_t n) {
-    _bcopy(src, dest, n);
+    bcopy(src, dest, n);
 
     return dest;
 }
diff --git a/src/code/z_scene_proc.c b/src/code/z_scene_proc.c
index 11e6fa832d..b7775e8680 100644
--- a/src/code/z_scene_proc.c
+++ b/src/code/z_scene_proc.c
@@ -454,7 +454,7 @@ void SceneProc_DrawSceneConfig6(GlobalContext* ctxt) {
     for (i = 0; i < 9; i++, dlHead += 2) {
         u32 lodFrac = 0;
 
-        _bcopy(D_801C3C88, dlHead, sizeof(Gfx[2]));
+        bcopy(D_801C3C88, dlHead, sizeof(Gfx[2]));
 
         switch(i) {
         case 0:
diff --git a/src/code/z_skelanime.c b/src/code/z_skelanime.c
index c85e83d8d2..4612cd33ee 100644
--- a/src/code/z_skelanime.c
+++ b/src/code/z_skelanime.c
@@ -1731,5 +1731,5 @@ void SkelAnime_Free(SkelAnime* skelAnime, GlobalContext* globalCtx) {
 }
 
 void SkelAnime_CopyVec3s(SkelAnime* skelAnime, Vec3s* dst, Vec3s* src) {
-    _bcopy(src, dst, sizeof(Vec3s) * skelAnime->limbCount);
+    bcopy(src, dst, sizeof(Vec3s) * skelAnime->limbCount);
 }
diff --git a/src/libultra/io/sptask.c b/src/libultra/io/sptask.c
index a731089125..394ce4bf23 100644
--- a/src/libultra/io/sptask.c
+++ b/src/libultra/io/sptask.c
@@ -5,7 +5,7 @@
 OSTask* _VirtualToPhysicalTask(OSTask* intp)
 {
     OSTask* tp = &tmp_task;
-    _bcopy((void*)intp, (void*)tp, sizeof(OSTask));
+    bcopy((void*)intp, (void*)tp, sizeof(OSTask));
     if (tp->t.ucode) {
         tp->t.ucode = (u64*)osVirtualToPhysical(tp->t.ucode);
     }
diff --git a/tables/functions.txt b/tables/functions.txt
index 5b5315cb77..41190224bb 100644
--- a/tables/functions.txt
+++ b/tables/functions.txt
@@ -23,10 +23,10 @@
     0x80080C90:("DmaMgr_SendRequest0",),
     0x80080D0C:("Dmamgr_Start",),
     0x80080E00:("Dmamgr_Stop",),
-    0x80080E30:("Yaz0_LoadFirstChunk",),
-    0x80080ED0:("Yaz0_LoadNextChunk",),
-    0x80080FF0:("Yaz0_Decompress",),
-    0x80081178:("Yaz0_LoadAndDecompressFile",),
+    0x80080E30:("Yaz0_FirstDMA",),
+    0x80080ED0:("Yaz0_NextDMA",),
+    0x80080FF0:("Yaz0_DecompressImpl",),
+    0x80081178:("Yaz0_Decompress",),
     0x80081250:("IrqMgr_AddClient",),
     0x800812DC:("IrqMgr_RemoveClient",),
     0x80081368:("IrqMgr_SendMesgForClient",),
@@ -408,7 +408,7 @@
     0x80091290:("__osGetCompare",),
     0x800912A0:("osDpGetStatus",),
     0x800912B0:("osDpSetStatus",),
-    0x800912C0:("_bcopy",),
+    0x800912C0:("bcopy",),
     0x800915D0:("__osResetGlobalIntMask",),
     0x80091630:("func_80091630",),
     0x80091808:("func_80091808",),
diff --git a/tables/objects.txt b/tables/objects.txt
index 64c8dcc035..d62038303f 100644
--- a/tables/objects.txt
+++ b/tables/objects.txt
@@ -3,7 +3,7 @@
     0x80080150:"idle",
     0x800805E0:"viconfig",
     0x80080790:"z_std_dma",
-    0x80080E30:"",
+    0x80080E30:"yaz0",
     0x80081250:"irqmgr",
     0x80081820:"CIC6105",
     0x80081920:"",
diff --git a/tables/variables.txt b/tables/variables.txt
index bba0ffe515..34138bc278 100644
--- a/tables/variables.txt
+++ b/tables/variables.txt
@@ -291,8 +291,12 @@
     0x8009B358:("dmamgrOSThread","OSThread","",0x1b0),
     0x8009B508:("dmamgrStack","u8","[1280]",0x500),
     0x8009BA08:("D_8009BA08","UNK_TYPE1","",0x1),
-    0x8009BA10:("yaz0FileBuffer","u8","[1024]",0x400),
-    0x8009BE10:("yaz0DecompStatus","Yaz0DecompState","",0x14),
+    0x8009BA10:("sYaz0DataBuffer","u8","[1024]",0x400),
+    0x8009BE10:("sYaz0CurDataEnd","u8*","",0x4),
+    0x8009BE14:("sYaz0CurRomStart","u32","",0x4),
+    0x8009BE18:("sYaz0CurSize","u32","",0x4),
+    0x8009BE1C:("sYaz0MaxPtr","u8*","",0x4),
+    0x8009BE20:("D_8009BE20","u8*","",0x4),
     0x8009BE30:("D_8009BE30","UNK_TYPE4","",0x4),
     0x8009BE34:("D_8009BE34","UNK_TYPE4","",0x4),
     0x8009BE38:("romInfoFaultClient","FaultClient","",0x10),
diff --git a/tools/preprocess.py b/tools/preprocess.py
index 01db33ba8d..c01fd2870d 100755
--- a/tools/preprocess.py
+++ b/tools/preprocess.py
@@ -32,8 +32,9 @@ opt_flags = [x for x in compile_args if x in ['-g', '-O2', '-framepointer', '-g3
 preprocessed_file = tempfile.NamedTemporaryFile(prefix='preprocessed', suffix='.c')
 
 if opt_flags != []:
-    subprocess.check_call(asm_processor + opt_flags + [in_file], stdout=preprocessed_file)
+    asmproc_flags = opt_flags + [in_file, '--input-enc', 'utf-8', '--output-enc', 'euc-jp']
+    subprocess.check_call(asm_processor + asmproc_flags, stdout=preprocessed_file)
     subprocess.check_call(compiler + compile_args + ['-I', in_dir, '-o', out_file, preprocessed_file.name])
-    subprocess.check_call(asm_processor + opt_flags + [in_file, '--post-process', out_file, '--assembler', assembler_sh, '--asm-prelude', prelude])
+    subprocess.check_call(asm_processor + asmproc_flags + ['--post-process', out_file, '--assembler', assembler_sh, '--asm-prelude', prelude])
 else:
     subprocess.check_call(compiler + compile_args + ['-I', in_dir, '-o', out_file, in_file])
\ No newline at end of file
diff --git a/undef.txt b/undef.txt
index 8d84389c34..3eafbaecd2 100644
--- a/undef.txt
+++ b/undef.txt
@@ -30,8 +30,12 @@ dmamgrMsqMessages = boot_bss_start + 0x00001DD8;
 dmamgrOSThread = boot_bss_start + 0x00001E58;
 dmamgrStack = boot_bss_start + 0x00002008;
 D_8009BA08 = boot_bss_start + 0x00002508;
-yaz0FileBuffer = boot_bss_start + 0x00002510;
-yaz0DecompStatus = boot_bss_start + 0x00002910;
+sYaz0DataBuffer = boot_bss_start + 0x00002510;
+sYaz0CurDataEnd = boot_bss_start + 0x00002910;
+sYaz0CurRomStart = boot_bss_start + 0x00002914;
+sYaz0CurSize = boot_bss_start + 0x00002918;
+sYaz0MaxPtr = boot_bss_start + 0x0000291C;
+D_8009BE20 = boot_bss_start + 0x00002920;
 D_8009BE30 = boot_bss_start + 0x00002930;
 D_8009BE34 = boot_bss_start + 0x00002934;
 romInfoFaultClient = boot_bss_start + 0x00002938;