transfer_From added but tests failiing

examples/erc20/contracts/ERC20.huff

@@ -50,11 +50,20 @@
     0x20 0x00 return
 }
 
+#define macro _ALLOWANCE() = takes (2) returns (1) {
+    // call stack [from,to]
+    LOAD_ELEMENT_FROM_KEYS(0x00)    // [value]
+
+    0x00 mstore
+
+    0x20 0x00 return
+}
+
 #define macro ALLOWANCE() = takes (0) returns (0) {
     0x24 calldataload       // [to]
     0x04 calldataload       // [from, to]
 
-    LOAD_ELEMENT_FROM_KEYS(0x00)    // [value]
+    _ALLOWANCE()    // [value]
 
     0x00 mstore
 
@@ -94,12 +103,17 @@
     [BALANCE_LOCATION] STORE_ELEMENT_FROM_KEYS(0x00) // [value, from, to]
 }
 
+#define macro _APPROVE() = takes (2) returns (0) {
+    // call stack [from, to , value]
+    STORE_ELEMENT_FROM_KEYS(0x00)
+}
+
 #define macro APPROVE() = takes (0) returns (0) {
     0x24 calldataload       // [value]
     0x04 calldataload       // [to, value]
     caller                  // [from, to, value]
 
-    STORE_ELEMENT_FROM_KEYS(0x00) 
+    _APPROVE()
 }
 
 #define macro TRANSFER() = takes(0) returns(1) {
@@ -127,6 +141,52 @@
         0x00 0x00 revert
 }
 
+#define macro TRANSFER_FROM() = takes (0) returns (0) {
+    0x04 calldataload       // [from]
+    0x24 calldataload       // [to, from]
+    0x44 calldataload       // [value, to, from]
+
+    dup2                    // [to, value, to, from]
+    dup4                    // [from, to, value, to, from]
+
+    // check if allowance > value
+    _ALLOWANCE()    // [allowance, value, to, from]
+    dup2                            // [value, allowance, value, to, from]
+    dup2                            // [allowance, value, allowance, value, to, from]
+    lt                              // [allowance < value, allowance, value, to, from]
+
+    // revert if allowance < value
+    error jumpi                     // [allowance, value, to, from] 
+
+    // update allowance
+    sub                              // [allowance-value, to, from]
+    swap2                              // [from, to, value]
+    dup3                             // [value,from,to,value]
+    dup3                             // [to,value,from,to,value]
+    dup3                            // [from,to,value,from,to,value]
+    _APPROVE()                          // [from,to,value]
+
+    transfer value
+    swap1                             // [to,from,value]
+    swap2                              // [value,from,to]
+    TRANSFER_TAKE_FROM(error)          // [value, from, to]
+    TRANSFER_GIVE_TO()                 // [value, from, to]
+
+    // Emit the transfer event.
+    // 0x00 mstore                 // [from, to]
+    // [TRANSFER_EVENT_SIGNATURE]  // [sig, from, to]
+    // 0x20 0x00                   // [0, 32, sig, from, to]
+    // log3                        // []
+
+    // Return "1" to represent a succesful transfer.
+    0x01 0x00 mstore
+    0x20 0x00 return 
+
+    // Error destination.
+    error:
+        0x00 0x00 revert
+}
+
 /* Mint Functions */
 #define macro MINT() = takes(0) returns (0) {
     // Ensure that the sender is the owner of the contract.
@@ -158,13 +218,16 @@
 #define macro MAIN() = takes(0) returns (0) {
     // Identify which function is being called.
     0x00 calldataload 0xE0 shr
+    dup1 0x23b872dd eq transferFrom jumpi
     dup1 0xa9059cbb eq transfer jumpi
     dup1 0x40c10f19 eq mints jumpi
     dup1 0x70a08231 eq balanceOf jumpi
     dup1 0x18160ddd eq totalSupply jumpi
     dup1 0x095ea7b3 eq approve jumpi
     dup1 0xdd62ed3e eq allowance jumpi
 
+    transferFrom:
+        TRANSFER_FROM()
     transfer:
         TRANSFER()
     mints:
@@ -177,5 +240,4 @@
         APPROVE()
     allowance:
         ALLOWANCE()
-
 }

examples/erc20/contracts/utils/HashMap.huff

@@ -45,7 +45,7 @@
     sstore                      // []
 }
 
-#define macro STORE_ELEMENT_FROM_KEYS(mem_ptr) = takes(2) returns (0) {
+#define macro STORE_ELEMENT_FROM_KEYS(mem_ptr) = takes(3) returns (0) {
     // Input stack: [key1, key2, value]
     GET_SLOT_FROM_KEYS(<mem_ptr>) // [slot, value]
     sstore                      // []

examples/erc20/test/erc20.t.js

@@ -53,4 +53,27 @@ describe("ERC20", () => {
 
     expect(newAllowance).to.equal(val);
   });
+
+  it("transfer from test", async () => {
+    await token.mint(owner, val);
+    // must fail without approval
+    // await expect(token.transferFrom(owner, user, 1)).to.be.reverted;
+
+    await token.approve(user, val);
+
+    let oldAllowance = await token.allowance(owner, user);
+
+    expect(oldAllowance).to.equal(val);
+
+    const toTransfer = val / 50;
+    // must succeed with half of val
+    await token.transferFrom(owner, user, val);
+
+    // allowance must get reduced
+    let newAllowance = await token.allowance(owner, user);
+    expect(newAllowance).to.equal(0);
+
+    // let userBal = await token.balanceOf(user);
+    // expect(userBal).to.equal(toTransfer);
+  });
 });