C51 Malloc
Revision as of 07:50, 6 July 2023 by Talcall (talk | contribs) (Talcall moved page Calculate Available RAM Address to C51 Malloc: libc)
uses r4 input to determine the size of the requested file in bytes; finds and returns the address of the first unused sect of data after 0x801df000 in blocks of 0x800. r4 values between 0x1 and 0x7ff all dedicate 1 block of space, but a block size request of 0x800 for example would require 2 blocks. this is accounted for. 00044414: 27bdfff8 addiu r29,r29,0xfff8 00044418: 00002821 addu r5,r0,r0 #r5 = 0 0004441c: 000432c2 srl r6,r4,0x0b #r6 = input >> 0xb (0x800 to 0x1) 00044420: 308407ff andi r4,r4,0x07ff # 00044424: 10800002 beq r4,r0,0x00044430 #branch if input && 0x07ff is 0 00044428: 34070001 ori r7,r0,0x0001 #r7 = 1 0004442c: 24c60001 addiu r6,r6,0x0001 #r6 = Ceil(input>>0xb) 00044430: 00002021 addu r4,r0,r0 #r4 = 0 00044434: 3c018005 lui r1,0x8005 00044438: 00240821 addu r1,r1,r4 0004443c: 9023e9d4 lbu r3,-0x162c(r1) #loads byte from 0x8004e9d4 + r4 00044440: 00000000 nop 00044444: 1460000a bne r3,r0,0x00044470 #branch if not 0 00044448: 0067102b sltu r2,r3,r7 #true if r3 < r7 0004444c: 14a00002 bne r5,r0,0x00044458 00044450: 00000000 nop 00044454: 00804021 addu r8,r4,r0 #r8 = r4 (largest address non-zero value in loop space?) 00044458: 24a50001 addiu r5,r5,0x0001 #r5 + 1 0004445c: 00a6102b sltu r2,r5,r6 #set true if r5 < Ceil(input>>0xb) 00044460: 1040000c beq r2,r0,0x00044494 #branch when looped Ceil(input>>0xb) times 00044464: 00000000 nop #remembers number of times looped (r5) 00044468: 08011120 j 0x00044480 0004446c: 24840001 addiu r4,r4,0x0001 #r4 + 1 00044470: 14400002 bne r2,r0,0x0004447c #branch if r3 < r7 00044474: 00002821 addu r5,r0,r0 #r5 = 0 00044478: 24670001 addiu r7,r3,0x0001 #r7 = byte + 1 0004447c: 24840001 addiu r4,r4,0x0001 #r4 + 1 00044480: 2c820040 sltiu r2,r4,0x0040 #set true if r4 < 0x40 (hardcoded safeguard?) 00044484: 1440ffeb bne r2,r0,0x00044434 #loop if still yet to loop 0x40 times 00044488: 00a6102b sltu r2,r5,r6 #set true if r5 < Ceil(input>>0xb) 0004448c: 14400010 bne r2,r0,0x000444d0 #branch if so 00044490: 00001021 addu r2,r0,r0 #r2 = 0 00044494: 10a0000a beq r5,r0,0x000444c0 #branch if looped 0 times 00044498: 00002021 addu r4,r0,r0 #r4 = 0 0004449c: 3c038005 lui r3,0x8005 000444a0: 2463e9d4 addiu r3,r3,-0x162c #r3 = 0x8004e9d4 000444a4: 01041021 addu r2,r8,r4 #r2 = r8 + r4 000444a8: 00431021 addu r2,r2,r3 #r2 = 0x8004e9d4 + r8 + r4 000444ac: a0470000 sb r7,0x0000(r2) #store largest value + 1 to all bytes equal to and larger than the encountered number's address, ignores ones before 000444b0: 24840001 addiu r4,r4,0x0001 #loop count 000444b4: 0085102b sltu r2,r4,r5 #set true if not looped r5 times 000444b8: 1440fffa bne r2,r0,0x000444a4 #loop above until all data spaces are filled with 1 000444bc: 00000000 nop 000444c0: 3c038001 lui r3,0x8001 000444c4: 8c630010 lw r3,0x0010(r3) #loads LBA pointer 000444c8: 000812c0 sll r2,r8,0x0b #r2 = r8 << 0xb 000444cc: 00431021 addu r2,r2,r3 #r2 + 801df000 + 0x800 * (largest encountered number + 1) 000444d0: 27bd0008 addiu r29,r29,0x0008 000444d4: 03e00008 jr r31 000444d8: 00000000 nop
