From a64024a13a5c612f5ee393b20c02d531f9a671c2 Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Sat, 11 May 2024 15:38:00 +0200
Subject: Initial commit

---
 main.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 main.c

(limited to 'main.c')

diff --git a/main.c b/main.c
new file mode 100644
index 0000000..c68fcbe
--- /dev/null
+++ b/main.c
@@ -0,0 +1,98 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <assert.h>
+
+inline uint32_t sign_extend(uint32_t word, uint32_t size)
+{
+    const uint32_t mask = 1U << (size - 1);
+    return (word ^ mask) - mask;
+}
+
+struct Instruction
+{
+    uint8_t  opcode;
+    uint8_t  rs1;
+    uint8_t  rs2;
+    uint8_t  rd;
+    uint8_t  funct3;
+    uint8_t  funct7;
+    uint32_t imm;
+};
+
+struct Instruction decode_r_type(uint32_t word)
+{
+    struct Instruction instruction = {0};
+    instruction.opcode =  word        & 0x7F;
+    instruction.rd     = (word >> 7)  & 0x1F;
+    instruction.funct3 = (word >> 12) & 0x07;
+    instruction.rs1    = (word >> 15) & 0x1F;
+    instruction.rs2    = (word >> 20) & 0x1F;
+    instruction.funct7 =  word >> 25;
+    return instruction;
+};
+
+struct Instruction decode_i_type(uint32_t word)
+{
+    struct Instruction instruction = {0};
+    instruction.opcode =  word        & 0x7F;
+    instruction.rd     = (word >> 7)  & 0x1F;
+    instruction.funct3 = (word >> 12) & 0x07;
+    instruction.rs1    = (word >> 15) & 0x1F;
+    instruction.imm    = sign_extend(word >> 20, 12);
+    return instruction;
+};
+
+struct Instruction decode_s_type(uint32_t word)
+{
+    struct Instruction instruction = {0};
+    instruction.opcode =  word        & 0x7F;
+    instruction.funct3 = (word >> 12) & 0x07;
+    instruction.rs1    = (word >> 15) & 0x1F;
+    instruction.rs2    = (word >> 20) & 0x1F;
+    instruction.imm    = sign_extend(((word >> 7) & 0x1F) | (word >> 25), 12);
+    return instruction;
+};
+
+struct Instruction decode_b_type(uint32_t word)
+{
+    struct Instruction instruction = decode_s_type(word);
+    instruction.imm = ((instruction.imm << 11) & 0x800) | (instruction.imm & 0xfffff7ff);
+    return instruction;
+};
+
+struct Instruction decode_u_type(uint32_t word)
+{
+    struct Instruction instruction = {0};
+    instruction.opcode =  word        & 0x7F;
+    instruction.rd     = (word >> 7)  & 0x1F;
+    instruction.imm    =  word        & 0xFFFFF000;
+    return instruction;
+};
+
+struct Instruction decode_j_type(uint32_t word)
+{
+    struct Instruction instruction = {0};
+    instruction.opcode =  word        & 0x7F;
+    instruction.rd     = (word >> 7)  & 0x1F;
+    instruction.imm    = sign_extend(
+        ((word & 0x80000000) >> 11) |
+        ((word & 0x000FF000) >> 0)  |
+        ((word & 0x00100000) >> 9)  |
+        ((word & 0x7FE00000) >> 20), 21);
+    return instruction;
+}
+
+struct Hart
+{
+    uint32_t pc;
+    uint32_t regs[32];
+};
+
+int main(int argc, char* argv[])
+{
+    uint32_t instruction = 0xfa728213;
+    struct Instruction instr = decode_i_type(instruction);
+    printf("%u %u %u\n", instr.rd, instr.rs1, instr.imm);
+    return EXIT_SUCCESS;
+}
-- 
cgit